The use of oocyte cryopreservation for fertility preservation in patients with sex chromosome disorders: a case series describing outcomes

Abstract

Purpose

Characterize outcomes among adolescents and young adults (AYAs) with sex chromosome disorders (SCDs) after oocyte cryopreservation (OC) consultation.

Methods

Retrospective case series of all AYA (< 25 years) patients with SCDs seen for OC consultation from 2011 to 2019 at a large, urban, academic fertility center. All AYA patients with an SCD seen for OC consult in the study time period were reviewed and included. Data collected included patient age, SCD type, number of patients who attempted OC, number of cycles attempted, and cycle outcomes.

Results

Twenty-two patients were included: 9 with Turner syndrome, 12 with mosaic Turner syndrome, and 1 with 47,XXX. Mean age at consult was 14.7 ± 3.5 years. Fourteen patients elected for OC: 5 with Turner syndrome, 8 with mosaic Turner syndrome, and 1 47,XXX who pursued 31 OC cycles total. Of those 14 patients, 10 underwent retrieval, 9 froze oocytes, and 8 froze mature (MII) oocytes. Seven patients underwent > 1 cycle and 7 had ≥ 1 cancelation. 3/3 patients who pursued cycles after 1st cancelation never got to retrieval. Age, SCD type, and baseline FSH did not predict ability to freeze MIIs. One patient returned after OC and attempted 4 ovulation induction cycles and 2 IVF cycles; all were canceled for low response.

Conclusions

AYA patients with SCDs have a high risk of poor response and cycle cancelation but the majority froze MIIs. Thus, setting expectations is important. A larger sample size is needed to evaluate possible clinical predictors of success.

Introduction

Sex chromosome disorders are the most common chromosomal disorders, affecting approximately 1 in 400 male and 1in 650 female newborns [1]. Turner syndrome is an example of a common sex chromosome disorder with a prevalence of approximately 1 in 2,000 females [2]. An estimated 50% of females with Turner syndrome have a monosomy X karyotype (45,X), 5–10% have a duplication of the long arm of one X chromosome, and the majority of the remainder have a mosaic karyotype with varying degrees of 45,X/46,XX/47,XXX in their cell lines [3]. Another common sex chromosome disorder is 47,XXX, affecting approximately 1 in 1,190 females, although it is likely underdiagnosed [2].

Women with Turner syndrome frequently experience an accelerated decline of ovarian reserve [4, 5]. Differences in degree of mosaic status among women with Turner syndrome may explain differences in ovarian follicular reserve. It is thought that the greater the degree of mosaicism, the more likely a patient is to undergo spontaneous puberty with menarche [6, 7] and retain fertility into adolescence or young adulthood [8, 9]. There are multiple case reports of pre-mature ovarian failure due to hypergonadotropic hypogonadism in those with 47,XXX; however, the exact incidence of pre-mature ovarian failure in women with 47,XXX is unknown, and it is thought that pubertal onset and sexual development are usually normal [10]. Nevertheless, all patients with sex chromosome disorders should receive counseling about the possibility of an early diminished ovarian reserve or insufficiency.

Given the high likelihood of premature ovarian insufficiency, women with sex chromosome disorders may present for consultation regarding fertility preservation at a younger age, such as in adolescence or young adulthood [5, 8, 11]. Ovarian tissue cryopreservation [12–15], in vitro maturation of oocytes [12, 13], and oocyte cryopreservation [14–21] are methods for fertility preservation in this population. Given that oocyte cryopreservation is (1) considered less invasive than ovarian tissue cryopreservation [17], (2) the technology and outcomes have improved [22], and (3) the experimental label was lifted in 2012, this method has received increasing attention for this population.

Optimal candidates for oocyte cryopreservation have gone through spontaneous puberty with menarche, have not exhausted their ovarian reserve, and have sufficient psychological maturity to understand the procedure [11, 17]. Unfortunately, only 5–20% of women with Turner syndrome undergo menarche [6, 7, 23, 24]. Additionally, even those who are candidates for oocyte cryopreservation may be unsuccessful in freezing mature oocytes. Thus, it is important to define predictors of oocyte cryopreservation success in this population, in order to accurately counsel and prepare patients. Prior studies have found that age [14], percent mosaicism [13, 14, 25], spontaneous pubertal development [25], and FSH [13, 14, 25] and AMH [13, 25] levels are associated with the presence of ovarian follicles.

Prior studies have demonstrated the feasibility of oocyte cryopreservation in this population [15–21]; however, many are case reports of one individual, and few have examined cohorts of patients such as the one presented here. Therefore, our primary objective for this study was to describe outcomes after oocyte cryopreservation consultation among girls with sex chromosome disorders. Our secondary objective was to determine predictors of oocyte cryopreservation success among those with sex chromosome disorders.

Methods

Study design and subjects

This is a retrospective case series of all adolescent and young adult (< 25 years) patients with sex chromosome disorders seen for oocyte cryopreservation consultation at a large, urban, academic fertility center from 2011 to 2019. All adolescent and young adult patients seen for consult regarding oocyte cryopreservation in the study time period were reviewed. Only those with a sex chromosome disorder were included. To increase overall sample size, patients were not excluded on the basis of missing variables (as some charts were paper and had since been moved off site) if they met inclusion criteria. It is important to note that during the study time period, oocyte tissue cryopreservation was not available at our center. The study was performed with NYU IRB approval (#s13-00389).

Variables

All included patients were individually reviewed by one researcher via the electronic medical record (EMR) to ensure uniform data collection. An independent researcher reviewed the collected data for accuracy. A discrete list of variables was constructed prior to chart review, and chart review followed a uniform structure for each patient. Variables collected from the EMR included the following: type of sex chromosome disorder; age at presentation; degree of pubertal development; Turner syndrome characteristics if applicable; pursuit of oocyte cryopreservation; age at oocyte cryopreservation cycle; AMH, FSH, and E2 at each oocyte cryopreservation cycle; number of oocyte cryopreservation cycles attempted; number of oocytes retrieved and frozen per retrieval; reasons for not undergoing oocyte cryopreservation; use of frozen oocytes for embryo transfer; and decision to undergo alternate assistive reproductive cycles such as in vitro fertilization.

Given that assessment and reporting of detailed mosaic status of Turner syndrome patients is a fairly recent addition to streamlining clinical practice at our center, there are patients in this cohort for whom screening for mosaicism was either unknown or not fully reported by the referring provider. These patients are categorized as having non-mosaic Turner syndrome with complete monosomy X (presumed karyotype 45,X) as this is the diagnosis that they were given at the time of assessment.

Primary outcomes included patient age at time of oocyte cryopreservation, type of sex chromosome disorder, number of patients who opted to undergo oocyte cryopreservation, number of oocyte cryopreservation cycles attempted, and cycle outcomes (including number of oocytes retrieved and frozen). The secondary outcome was whether age, sex chromosome disorder type, and day two FSH predicted ability to freeze mature oocytes (MIIs).

All patients were assigned a number from one through 22 at the study outset. All references to patient numbers are consistent across tables and written results.

Ovarian stimulation, oocyte retrieval, and oocyte cryopreservation protocols

Controlled ovarian hyperstimulation utilizing a GnRH antagonist protocol with administration of gonadotropins was prescribed for each patient based on their antral follicle count, age, FSH level, and AMH level as determined by their physician. No patients were medicated with estrogen or hormone containing birth control prior to controlled ovarian hyperstimulation start with the exception of patient seven who was on estrogen prior to her cycle. Follicular growth and maturation were monitored by transvaginal or transabdominal ultrasound based on patient comfort level as well as serum estradiol (E2) level. The GnRH antagonist was added when a lead follicle was identified as 13 mm or greater or the E2 was greater than 1000 pg/mL. According to provider preference, either hCG alone or hCG with leuprolide acetate was used for trigger of final follicular maturation when at least two follicles sized 18–19 mm were seen, with planned oocyte aspiration scheduled for 35 h after administration. Oocyte retrieval was performed via ultrasound-guided transvaginal aspiration.

Oocytes were cryopreserved via slow freeze or vitrification, as previously described [26], as appropriate based on the lab technology utilized at time of aspiration. At our center, immature oocytes (MI and GV) are routinely frozen in this population given the high likelihood of depletion of ovarian reserve in the near future. Some oocytes, such as those with a fractured zona pellucida or atretic oocytes, were not frozen based on laboratory protocol.

All patients and family members (where appropriate) received counseling from their reproductive endocrinologist before, during, and after each oocyte cryopreservation cycle, and all patients were provided with the option to speak with a mental health professional. Patients were thoroughly counseled on the risk of non-response, cancelation, and no or few oocytes being retrieved.

Statistical analysis

All continuous variables were assessed for normality via a Kolmogorov-Smirnoff test. Parametric descriptive data are presented as mean ± standard deviation, while non-parametric descriptive data are presented as median with range. Levels that resulted with a “ < ” symbol were round to their nearest tenth (ex: < 0.16 as 0.16) for use in statistical analysis. Statistical analysis included multiple logistic regression to determine whether age, type of sex chromosome disorder, and FSH level at cycle start significantly predicted ability to freeze MIIs. Data analysis was conducted in SPSS (v.25), with p < 0.05 considered significant.

Results

Patient characteristics

In total, 22 patients were included in our analysis. Of the study participants, 9 had non-mosaic Turner syndrome (45,X), 12 had mosaic Turner syndrome (45,X/46,XX/47,XXX), and 1 had 47,XXX (Tables 1 and 2). Of note, four patients were classified as having non-mosaic Turner syndrome (45,X) but their mosaic status was unknown at the time of fertility preservation consultation (patients 4, 6, 15, and 17). The average age at presentation for consultation was 14.7 ± 3.5 years (range 8–21). Among Turner syndrome patients (both with and without mosaicism), the most common phenotypic characteristic present was short stature, which was noted in 12 of the 22 patients (55%). Two patients were also noted to have hypothyroidism, one patient was noted to have a webbed neck, and one patient was noted to have growth delay (Tables 1 and 2). Of the 22 patients, 12 (55%) were noted to have undergone menarche and 5 were noted to have breast development (Tables 1 and 2).

Table 1.

Baseline characteristics of all study participants including age at presentation for oocyte cryopreservation consultation, type of sex chromosome disorder (TS, Turner syndrome), presence of Turner syndrome characteristics, presence of breast development, presence of menarche, and highest recorded historical FSH value. Menstrual patterns are presented if known. *Patients whose mosaic status was not confirmed. This table refers to patients who elected to undergo oocyte cryopreservation

Patient ID	Age at first cycle	Sex chromosome disorder	Turner syndrome characteristics	Breast development yes/no	Menstruation yes/no	Historic FSH (mIU/ml)
1	13	Mosaic TS	Short stature	Unknown	Yes	6.9
2	14	TS	Short stature	Unknown	No	Unknown
3	14	Mosaic TS	Short stature	Unknown	Yes, regular	5.2
4	14	TS*	Short stature	Yes	Yes	66.4
5	15	TS	Unknown	Unknown	Unknown	Unknown
6	15	TS*	Unknown	Unknown	Unknown	Unknown
7	15	Mosaic TS	Short stature	Unknown	Yes, previously regular now amenorrheic	74
8	16	Mosaic TS	Short stature	Yes	Yes, regular	Unknown
9	16	47XXX	N/A	Yes	Yes, regular	Unknown
10	17	Mosaic TS	Short stature, hypothyroidism	Unknown	Yes	Unknown
11	18	Mosaic TS	Unknown	Unknown	Unknown	Unknown
12	21	Mosaic TS	Short stature	Unknown	Yes	4
13	21	TS	Short stature, webbed neck	Unknown	Yes, irregular	4.1
14	21	Mosaic TS	None	Yes	Yes	6.3
Mean ± SD	16.4 ± 2.8

Table 2.

Baseline characteristics of all study participants including age at presentation for oocyte cryopreservation consultation, type of sex chromosome disorder (TS, Turner syndrome), presence of Turner syndrome characteristics, presence of breast development, presence of menarche, and highest recorded historical FSH value. Menstrual patterns are presented if known. *Patients whose mosaic status was not confirmed. This table refers to patients who, to date, have not undergone oocyte cryopreservation

Patient ID	Age at presentation	Sex chromosome disorder	Turner syndrome characteristics	Breast development yes/no	Menstruation yes/no	Historic FSH (mIU/ml)	Reason for not cycling
15	8	TS*	Short stature, sweating, lost teeth early	Unknown	Unknown	Unknown	No follow-up
16	10	Mosaic TS	Unknown	Yes	Unknown	2.23	High AMH so no need for immediate fertility preservation per provider. Plan for age 16
17	11	TS*	Unknown	Unknown	Unknown	Unknown	Unknown
18	11	TS	Unknown	Unknown	No	1.4	Wait until menarche
19	11	Mosaic TS	Short stature, hypothyroidism	Yes	No	16	High FSH, no menarche, limited pubertal changes
20	13	TS	Short stature	Yes	No	80	High FSH
21	14	Mosaic TS	None	Unknown	Yes, irregular	Unknown	Unknown
22	16	Mosaic TS	Growth delay	Unknown	Yes	3.7	Patient planning to cycle and will schedule when school allows
Mean ± SD	11.8 + 2.5

In total, 64%, or 14 of the 22 patients who had a consultation, elected to undergo at least one cycle of oocyte cryopreservation. Five had non-mosaic Turner syndrome, 8 had mosaic Turners syndrome, and 1 had 47,XXX (Fig. 1). The average age of patients who pursued oocyte cryopreservation was 16.4 ± 2.8 years (Tables 1 and 2). Of note, 10 of the 14 patients who opted to undergo oocyte cryopreservation had experienced menarche (Tables 1 and 2). Three of the patients had regular menstrual periods, two had irregular menstrual periods, and one patient previously had regular menstrual periods but experienced amenorrhea after approximately 2 years. Two patients, numbers four and seven, had a known history of elevated FSH levels (Tables 1 and 2).

Fig. 1.

Number of patients with Turner syndrome (TS), Turner syndrome mosaicism (TSM), and 47XXX who elected to undergo oocyte cryopreservation (OC) and cycle outcomes

The average age of those who did not undergo oocyte cryopreservation was 11.8 ± 2.5 years (Tables 1 and 2). Among the 8 patients who did not pursue oocyte cryopreservation, the most common reasons were high FSH and lack of menarche. Patient 16 was advised that given her high AMH she should monitor her AMH every 6 months, with a plan to pursue oocyte cryopreservation at age 16 so long as her AMH did not begin to drop in the interim. Patient 22 elected to pursue oocyte cryopreservation, but had not yet begun a cycle due to scheduling conflicts with school.

Oocyte cryopreservation cycle outcomes

The 14 patients who chose to undergo oocyte cryopreservation completed a total of 31 cycles. The median number of cycles was 1.5 with a range of 1–9 (Table 3). Ten patients (71%) ultimately underwent retrieval, 9 patients (64%) successfully froze oocytes, and 8 patients (57%) froze at least one MII oocyte. There was a median of 9 oocytes retrieved (range 0–22), 9 oocytes frozen (range 0–21), and 5 MII oocytes frozen (range 1–16) per patient (Table 3). Six of the 14 patients (43%) froze > 10 MIIs, and among those who successfully froze MIIs the median number frozen was 13 (range 2–16).

Table 3.

Summary of patient outcomes among patients who elected to undergo oocyte cryopreservation, including age at first oocyte cryopreservation cycle, type of sex chromosome disorder, hormonal measurements at first oocyte cryopreservation cycle, number of cycle attempts, number of oocyte retrievals, and total number of oocytes retrieved and frozen.

Patient ID	Age at first cycle	Sex chromosome disorder	E2 (pg/mL) at first cycle	FSH (mIU/mL) at first cycle	AMH (ng/ml)	# of oocyte cryopreservation attempts	# of retrievals	Total oocytes retrieved	Total oocytes frozen	MII oocytes frozen	MI oocytes frozen	GV oocytes frozen
1	13	Mosaic TS	38	5.2	2.99	1	1	14	14	12	2	0
2	14	TS	41	0.4	< 0.16	1	1	4	4	2	1	1
3	14	Mosaic TS	27	4.5	2.08	1	1	21	21	16	3	2
4	14	TS*	23	20.6	0.03	3	0	0	0	0	0	0
5	15	TS	23	3.9	Unknown	2	0	0	0	0	0	0
6	15	TS*	30	0.2	Unknown	1	1	15	15	15	0	0
7	15	Mosaic TS	109	1.8	< 0.003	1	0	0	0	0	0	0
8	16	Mosaic TS	< 20	0.5	1.63	3	2	19	18	8	6	4
9	16	47XXX	44	3.3	1.04	2	2	22	18	16	0	2
10	17	Mosaic TS	49	1.1	Unknown	9	4	3	3	0	3	0
11	18	Mosaic TS	35	< 0.1	Unknown	2	0	0	0	0	0	0
12	21	Mosaic TS	80	6.5	2.6	1	1	22	21	12	4	5
13	21	TS	21	9.3	< 0.03	3	2	2	0	0	0	0
14	21	Mosaic TS	42	5.4	5.34	1	1	19	19	14	0	5
Median (range) or mean ± SD	16.4 ± 2.8		36.5 (20–109)	4.5 ± 5.4	1.6 + 1.7	1.5 (1–9)	1 (0–4)	9 (0–22)	9 (0–21)	5 (0–16)	0 (0–6)	0 (0–5)

TS Turner syndrome; MII, mature oocyte; MI, immature oocyte; GV, germinal vesicle. *Patients whose mosaic status was not confirmed

Seven patients (50%) underwent more than one oocyte cryopreservation cycle (Table 4), and 7 patients (50%) had at least one cancelation or no-start (Table 4). For the majority of patients, the reason behind cancelation was multifactorial; however, the most common factor was poor ovarian response. Of the nine patients who froze oocytes, all retrieved oocytes on their first cycle, and three then chose to undergo further cycles. Of the three patients who retrieved zero oocytes on their first cycle and chose to pursue additional cycles, all three did not retrieve oocytes on subsequent cycles (Table 4).

Table 4.

Summary of outcomes for each cycle performed among patients who elected to undergo oocyte cryopreservation. *Patients whose mosaic status was not confirmed. ′Cycle cancelation or no start. †Medicated cycle. TS, Turner syndrome;

Patient ID	Sex chromosome disorder	Cycle #	Age at cycle start (yrs)	Total oocytes retrieved per cycle	Total oocytes frozen per cycle	M2s frozen per cycle	M1s Frozen per cycle	GVs frozen per cycle
1	Mosaic TS	1	13	14	14	12	2	0
2	TS	1	14	4	4	2	1	1
3	Mosaic TS	1	14	21	21	16	3	2
4	TS*	1′ 2′ 3′	14 14 15	0 0 0	0 0 0	0 0 0	0 0 0	0 0 0
5	TS	1′ 2′	15 16	0 0	0 0	0 0	0 0	0 0
6	TS*	1	15	15	15	15	0	0
7	Mosaic TS	1′†	15	0	0	0	0	0
8	Mosaic TS	1 2 3′	16 16 19	9 10 0	9 9 0	5 3 0	2 4 0	2 2 0
9	47XXX	1 2	16 16	6 16	6 12	5 11	0 0	1 1
10	Mosaic TS	1 2′ 3′ 4′ 5 6′ 7 8′ 9	17 17 18 18 18 19 19 19 20	1 0 0 0 1 0 0 0 1	1 0 0 0 1 0 0 0 1	0 0 0 0 0 0 0 0 0	1 0 0 0 1 0 0 0 1	0 0 0 0 0 0 0 0 0
11	Mosaic TS	1′ 2′	18 19	0 0	0 0	0 0	0 0	0 0
12	Mosaic TS	1	21	22	21	12	4	5
13	TS	1 2′ 3	21 21 21	1 0 1	0 0 0	0 0 0	0 0 0	0 0 0
14	Mosaic TS	1	21	19	19	14	0	5
Median (range) or mean ± SD			17.3 ± 2.5	0 (0–22)	0 (0–21)	0 (0–16)	0 (0–4)	0 (0–5)

MII, mature oocyte; MI, immature oocyte; GV, germinal vesicle

At the time of this study, none of the 14 patients has returned to use their cryopreserved oocytes to create embryos and their oocytes all remain frozen. However, patient #10 returned with a partner and attempted four cycles of ovulation induction and two cycles of in vitro fertilization at the ages of 21–24. All cycles were canceled for low response and she was counseled against further cycles. She has not yet thawed her oocytes.

Predictors of mature oocyte cryopreservation

Among those with mosaic Turner syndrome, 75% (6/8) froze oocytes, while among those with non-mosaic Turner syndrome 40% (2/5) froze oocytes. Additionally, one of the patients who froze oocytes and was classified as having non-mosaic Turner syndrome, patient six, was not screened for mosaicism leaving open the possibility that she has mosaic cell lines. It is notable that there was a wide range of day two FSH values among those who underwent oocyte cryopreservation (< 0.1–20.6 mIU/mL). Only patient number 4 had a high FSH (all three of her cycles were canceled for low response), and four patients had an FSH < 1mIU/mL (Table 3). However, age, type of sex chromosome disorder, and day two FSH did not predict ability to freeze MIIs (p > 0.5 for all variables) (Table 5). It is also worth noting that two patients (patients four and seven) had a known history of elevated FSH, and neither of these patients successfully retrieved or froze oocytes. Additionally, of the AMH data available, all pts > 1 ng/mL froze MIIs (Table 3).

Table 5.

Regression table for a multiple logistic regression model examining whether age, type of sex chromosome disorder (either Turner syndrome, Turner syndrome mosaicism, or 47XXX), and FSH level at cycle start predict ability to freeze at least one MII oocyte

Variable	B	S.E	Wald	df	p-value	Exp(B)
Age	− 0.82	0.22	0.14	1	0.708	0.921
Sex chromosome disorder	1.056	1.115	0.895	1	0.344	2.873
FSH	− 0.82	0.132	0.386	1	0.534	0.921
Constant	0.214	3.738	0.003	1	0.954	1.239

Discussion

Oocyte cryopreservation outcomes

Our results indicate that oocyte cryopreservation is an important option to consider in adolescents and young adults with sex chromosome disorders who desire genetic offspring. In our cohort of 14 patients who underwent oocyte cryopreservation, 64% successfully froze oocytes and 57% froze mature (MII) oocytes. The median number of MIIs frozen was 5 (range 0–16), with 6 of the 14 patients freezing > 10 MIIs. While half of patients experienced a cancelation or no start, the fact that over 50% of patients froze MIIs is encouraging evidence that oocyte cryopreservation is a feasible option in this population. However, it is important to note that two clusters of patients emerged in our data set: 8 patients who froze MIIs with a median of 13 MIIs frozen, and 6 patients who froze 0 MIIs. Thus, it is important to set expectations prior to oocyte cryopreservation and counsel patients appropriately.

Our results are concordant with multiple studies demonstrating that oocyte cryopreservation is feasible in women with Turner syndrome. Several case reports have been published describing women with mosaic Turners syndrome aged, 28, 16, 14, 22, and 28, who froze 7, 2, 12, 8, and 13 oocytes, respectively [15–19]. Balen et al. examined oocytes from their patient and found them to be morphologically and chromosomally normal [15]. The case presented by Oktay et al. was subsequently reported again alongside two 13-year-old girls with mosaic Turner syndrome who underwent oocyte cryopreservation, and who froze 10 and 12 mature oocytes [20]. Talaulikar et al. describe a cohort of 7 women with mosaic and non-mosaic Turner syndrome aged 18–26, who cryopreserved an average of 9 oocytes [21]. Vergier et al. report on three women with mosaic and non-mosaic Turner syndrome aged 17–27 who cryopreserved an average of 15.3 oocytes [27]. Indeed, Grynberg et al. state that “oocyte cryopreservation after controlled ovarian hyperstimulation probably represents the best option for preserving fertility in post-menarchal girls [with Turner Syndrome]” [8], and Oktay et al. suggests that “all post-menarchal girls with TS be evaluated for ovarian reserve assessment and… counseled regarding oocyte cryopreservation as a viable fertility preservation option” [11].

As reflected in these recommendations, all of the patients in the examples above went through spontaneous puberty with menarche. Oktay and Bedoschi suggest an algorithm for fertility preservation in those with Turner syndrome, in which pre-pubertal girls are monitored for signs of declining ovarian reserve. If AMH remains high, oocyte cryopreservation is performed at an appropriate age post-puberty. If there is decline in AMH before puberty, ovarian tissue cryopreservation and in vitro maturation of oocytes should be considered [28]. It is worth noting, however, that patient #2 in our cohort was pre-menarchal and successfully froze MIIs (albeit only 2) with an AMH of < 0.16. Azem et al. recently reported the case of a 7-year old pre-pubertal girl with mosaic Turner syndrome who underwent oocyte cryopreservation and froze 6 MIIs [29]. Thus, oocyte cryopreservation could be considered among the appropriate candidate pre-menarchal girls who wish to preserve fertility without undergoing laparoscopy.

It is also worth noting that while most prior successful case reports of oocyte cryopreservation involved patients with mosaic Turner syndrome, two patients with non-mosaic Turner syndrome successfully froze MIIs in our cohort. Their success is consistent with prior accounts demonstrating the possibility of pregnancy in women with non-mosaic Turner syndrome [30], and with the case studies that included women with non-mosaic Turner syndrome cited above [21, 27]. Yet this result must be interpreted with caution, given that our data encompasses a period of time in which karyotyping for mosaicism was not routine practice at our center. Thus, patient six, who froze 15 MIIs and was categorized as having non-mosaic Turner syndrome, may have been categorized as mosaic had a full karyotype analysis been available.

Finally, it is encouraging that the patient with 47,XXX underwent two successful retrievals and froze 18 MIIs. As far as we are aware, this is the first study to examine oocyte cryopreservation outcomes in a patient with 47, XXX, and the results suggest that this could be a good method for fertility preservation in these patients.

Predictors of mature oocyte cryopreservation

The two distinct outcome clusters, as described above, that emerged in our study underline the importance of understanding predictors of oocyte cryopreservation success prior to attempted cycles. While type of sex chromosome disorder was not significantly associated with ability to freeze MII oocytes in a logistic regression, it is notable that a greater proportion of those with mosaic Turner syndrome (75%) froze oocytes versus those with non-mosaic Turner syndrome (40%). Again, it must be noted that not all patients in this study who carried a diagnosis of non-mosaic Turner syndrome were evaluated at a time when evaluating for mosaicism was routine at our center, and it has been postulated that the prevalence of mosaic karyotypes is higher than previously suspected [31]. Mosaic karyotype has been shown to be predictive of spontaneous pregnancy among women with Turner syndrome [23, 32] and is significantly associated with presence of ovarian follicles [13, 14, 25].

It has been noted that hormonal markers such as FSH may not be accurate predictors of ovarian reserve in girls and adolescents with Turner syndrome, as the hypothalamic–pituitary–adrenal axis is immature [8, 33], and should be interpreted with caution. We did not see a statistical association between day two FSH and ability to freeze MIIs; however, multiple studies [13, 14, 25] have noted an association between lower FSH levels and presence of ovarian follicles, and another concluded that baseline FSH is associated with oocyte cryopreservation success [27]. The discrepancy in conclusions may provide further evidence that the prognostic value of FSH in this population is unclear. However, this is not to suggest that individuals with a high FSH have an equal probability of successfully freezing oocytes as those with an FSH in the normal range (indeed, our patient with an elevated day two FSH did not freeze any oocytes nor did our patients with a history of elevated FSH), and these patients should be counseled appropriately.

AMH, on the other hand, has been shown to predict premature ovarian failure in women with Turner syndrome with high sensitivity [9, 34]. We were unable to evaluate the predictive value of AMH with regard to freezing MIIs because of unavailable data, but multiple studies [13, 25] have concluded that AMH is associated with follicle count in patients with Turner syndrome.

Concordant with this study, Mamsen et al. and Birgit et al. found no statistically significant correlation between age and follicle density among girls with Turner syndrome who underwent ovarian tissue cryopreservation [13, 25]. Hreinsson et al., on the other hand, did note higher numbers of follicles in younger girls [14]. It seems likely that the ideal time for fertility preservation in this population exists at the intersection of the patient’s age and karyotype, with those with a higher degree of mosaicism having a longer window in which to preserve fertility. Thus, we suggest that patients with Turner syndrome present for evaluation for oocyte cryopreservation as young as possible, such that those with who need immediate treatment can be seen in time, and others can be monitored and treated when appropriate.

Further considerations

Importantly, women with Turner syndrome have an increased risk of multiple life-threatening maternal complications during pregnancy [35]. Of particular importance is the increased risk of aortic dissection and rupture during pregnancy in this population, as 23–50% of these patients have cardiovascular malformations [36]. It is estimated that the risk of aortic dissection or rupture during pregnancy in women with Turner syndrome is as high as 2%, and death during pregnancy is increased by as much as 100-fold [37]. It is thus imperative that women with Turner syndrome are thoroughly screened for cardiovascular contraindications to pregnancy, counseled regarding the risks of pregnancy, and are closely monitored should they become pregnant [37, 38].

There is also an increased risk of spontaneous abortion and aneuploidy in this population [11, 28, 39, 40]. Borini and Coticchio point out that women with Turner syndrome may thus need upwards of 20 cryopreserved oocytes to have a high likelihood of live birth, and that there is limited evidence regarding the health and quality of oocytes from patients with Turner syndrome after warming [41]. Thus, it is also imperative that all women with Turner syndrome who seek fertility preservation strategies are accurately counseled regarding the risks of pregnancy, the use of both gestational carriers and pre-implantation genetic screening in their population, and the possibility of failure to conceive even after oocyte cryopreservation, and are thoroughly screened and counseled about contraindications to pregnancy [35, 37].

Strengths and limitations

A strength of this study is its large sample size relative to what has been previously published as well as its inclusion of all patients who presented for consultation about oocyte cryopreservation. Our study has several limitations. First and foremost is the retrospective study design and reliance on information recorded in the EMR. Several data points are missing for many of the patients including historic FSH, AMH, pubertal status and menstrual pattern, and presence of detailed Turner syndrome characteristics. Detailed karyotype information is not listed for mosaic participants as it was unavailable for the majority of patients. Future research endeavors should include detailed information about percent mosaicism. Detailed information regarding pre-stimulation evaluation that was conducted by other providers was not available in our separate electronic medical record. Additionally, although the sample size is large compared to previously published work, the sample still may not be large enough to be powered to draw conclusions. It is also a limitation that there was only one patient with 47,XXX in the study. The most important limitation of this study concerns the categorization of patients as Turner syndrome or Turner syndrome mosaic. It is possible that some of the patients who were categorized as Turner syndrome are, in fact, mosaic, but were assessed before full karyotype analysis became routine practice at our center. Thus, conclusions regarding patients who are categorized as non-mosaic Turner syndrome should be interpreted with caution.

Future directions

Further study with a larger sample size, detailed karyotype information, and detailed information on menstrual patterns (including duration from onset of menarche to time of treatment) is needed to elucidate clinical predictors of oocyte cryopreservation success among women with sex chromosome disorders. Further study is also needed to determine the frequency of oocytes with a normal karyotype retrieved from women with sex chromosome disorders. Additionally, further studies are needed to determine pregnancy and birth outcomes among women with sex chromosome disorders who freeze oocytes and subsequently choose to proceed with fertilization of oocytes and embryo transfer. These studies will aid in determining the optimal number of frozen oocytes needed to achieve clinical pregnancy and live birth, and whether freezing immature oocytes and in vitro maturation of oocytes are of value in this unique population where pregnancy is also high risk. Future studies should also examine the psychological impact of freezing oocytes in this population, and specifically whether being offered oocyte cryopreservation, whether successful or unsuccessful, leads to long-term psychological benefit or harm. Additionally, studies should be conducted to examine how best to counsel these patients such that any potential psychological impact is approached appropriately.

Conclusions

Oocyte cryopreservation is a viable means of preserving fertility and allowing the opportunity for genetic offspring among adolescents and young adults with sex chromosome disorders, as over half of patients in our cohort who underwent oocyte cryopreservation successfully froze mature oocytes. However, the risk of poor response and cycle cancelation remains high, and appropriate counseling and setting expectations are important. Additionally, much remains unknown regarding potential pregnancy and birth outcomes after oocyte cryopreservation in this population, and patients must be counseled about the possibility of lack of success from their cryopreserved oocytes. Providers should refer patients with sex chromosome disorders for oocyte cryopreservation consultation as young as possible, in line with clinical practice guidelines [38]. Further study with a larger sample size is needed to evaluate possible clinical predictors of oocyte cryopreservation success in this population.

Declarations

The authors declare no competing interests.