First trimester obstetric outcome of frozen thawed embryo transfer: does the stage of embryo make any difference?

Abstract

Background

The direction of management and outcome of frozen thawed embryo transfer (FET) is becoming different day by day with the invention of newer technologies and application of it as a treatment modality in modern medicine. It also contributes to around 25% of births because of Assisted Reproductive Technology (ART) procedures worldwide today.

Methods

A prospective longitudinal study was conducted at ART Center of tertiary care hospital. Couples with infertility planned to undergo FET were included in the study. Following FET, all positive cases were followed up till 14 weeks period of gestation. Data were collected and analyzed with appropriate statistical test using Epitable, 6.04 version, and SPSS, version 18, software.

Results

During the study period, a total of 470 FET cycles were carried out, and 1108 cryopreserved embryos were subjected to thawing procedure. Overall survival rate of 93.86% was noted. Among various stages of embryos thawed, the lowest survival rate (64.62%) was found in blastocyst group. Biochemical pregnancy rate, clinical pregnancy rate, and ongoing pregnancy rate were also analyzed in different subgroup of transferred embryos. The blastocyst group showed best implantation and clinical pregnancy rate but lowest survival rate among all subgroup of embryos.

Conclusion

The blastocyst transfer during FET cycle showed best clinical and ongoing pregnancy rate. So if clinical situations were favorable for blastocyst stage transfer, the same should be preferred for FET cycle.

Introduction

Pregnancy is an important event of married life leading to procreation. Infertility, on the other hand has troubled the mankind since ages. Assisted reproductive technologies (ARTs) have helped to achieve fertility in these cases. Frozen thawed embryo transfer (FET) cycle is a kind of ART where cycle monitoring is done to transfer frozen thawed embryo(s).¹ In 1983, first successful pregnancy after FET was reported.² Since then cryopreservation of embryos has been an accepted important technique for infertility treatment. Elective cryopreservation of all fresh embryos has also been proposed by many in special circumstances such as severe Ovarian Hyperstimulation Syndrome (OHSS).³ Embryo cryopreservation is an additional clinical safety in the presence of ovarian hyper stimulation. It also helps to lower the risk of multifetal gestation by reducing the need for multiple fresh embryos transfer.⁴

According to recent data from International Committee for Monitoring Assisted Reproductive Technologies, world report and European register by ESHRE have showed that the proportion of FETs to all initiated ART cycles was 27.4% and 28% respectively.5, 6 But over the last 30 years, there were lots of debate and questions on the survival rate of cryopreserved frozen embryos and pregnancy rate following FET. In this context, we have conducted a study on first trimester obstetric outcome of FET cycle. The aim and objective of the study was to see the (i) survival rate of frozen embryos, (ii) pregnancy rate, (iii) biochemical pregnancy rate, (iv) clinical pregnancy rate, (v) ongoing pregnancy rate, and (vi) other first trimester events such as miscarriage, ectopic, and multiple pregnancy in different stages of embryo transfer cycle following cryopreservation.

Materials and methods

Study design

A prospective longitudinal study.

Duration of study

01 Oct 2013 to 01 Mar 2015.

Study population

The study population comprised of the patients coming to ART Center of the tertiary care hospital. During the study period, a total number of 470 patients underwent FET cycle.

Inclusion and exclusion criteria

All patient underwent FET during the study period were included in the study.

Place of study

Assisted Reproductive Technology Center of the tertiary care hospital affiliated to Medical College, Pune.

Statistical analysis

All statistical analyses pertaining to study were carried out by Epitable, version 6.04, software and SPSS, version 18, software.

Definition of variables

Survival rate—Proportion of embryos survived the thawing process and subsequent grading of cleavage or blastocyst embryo.4, 7 The number of gestational sacs seen on Ultrasonography (USG) divided by the number of embryos transferred is termed as implantation rate.¹ Biochemical pregnancy is the pregnancy diagnosed by the detection of β-hCG in serum and that did not develop into a clinical pregnancy.¹ Clinical Pregnancy was considered as the detection of one or more gestational sacs (intrauterine or ectopic) on ultrasonography or definitive clinical signs of pregnancy. Detection of multiple gestational sacs in one individual was considered as one clinical pregnancy.¹ Ongoing pregnancy was considered at that pregnancy which was viable after 14 week period of gestation (POG), and these cases were transferred to Ante Natal Care Out-Patient Department (ANC OPD) of the affiliated Hospital. Other first trimester obstetric outcomes measured were ectopic pregnancy, miscarriage, or early pregnancy loss in form of missed abortion and spontaneous abortion and multiple pregnancy—in form of twin or higher order pregnancy.

Methodology

All patients planned to undergo FET during evaluation at ART Center were recruited under the study after obtaining the informed written consent. The approval of the institutional ethics committee was obtained prior to recruitment of study population. All FET cycles were carried out with hormone replacement cycle. On day 2 of menstrual cycle, all patients were supplemented with tablet estradiol valerate 2 mg twice daily for 5 days followed by 2 mg thrice daily for next 5 days. On day 12, with endometrium thickness between 9 and 11 mm, they were given Inj micronized progesterone 100 mg intramuscular daily till further advice. Thereafter, depending on the cell stage of embryos cryopreserved, FET was carried out. In case of blastocyst transfer, FET was carried out after 5 days of Inj progesterone supplementation. In case of 2 cell, 4 cell, or 8 cell stage embryos, the FET was carried out on day 2, 3, or 4 respectively. The serum β-hCG test was carried out on day 18 after transfer, and any value more than 5 IU/L was considered pregnancy positive. On day 21 after transfer, all patients were reviewed for transvaginal sonography. Localization of gestational sac in intrauterine or adnexa confirmed the clinical pregnancy. All cases of clinical pregnancy were continued with Inj progesterone and tablet dydrogesterone 10 mg twice daily. Subsequently, all cases of clinical pregnancy were followed till 14 weeks POG for adverse pregnancy outcome such as ectopic pregnancy, miscarriage, and multiple pregnancy. A total number of 470 patients were recruited as study population. Fig. 1, Fig. 2 shows the graphical representation and distribution of study population.

Fig. 1.

Distribution of study population.

Fig. 2.

Age distribution of study population.

Results

During the study period, a total number of 470 cases were initiated for FET cycle. Three cases were abandoned as no embryo survived the thawing on the day of transfer. In rest 467 cases, FET was carried out. Total study population has been grouped into four subtype depending on the cell stage (i.e. 2 cell, 4 cell, 8 cell, and blastocyst). The mean age of the study population was 27.97 ± 2.672 (1 standard deviation [SD]) yrs with range from 21 to 38 yrs. The mean age of 2 cell, 4 cell, 8 cell, and blastocyst were 27.67 ± 2.531, 27.97 ± 2.784, 28.16 ± 2.575, and 27.30 ± 2.672 yrs, respectively. The median age of total study population and subgroups were 28 yrs, and mean age of total study population and all subgroup did not have any significant statistical difference with p value 0.404 (Fig. 2, Fig. 3).

Fig. 3.

Histogram of age distribution of different study subgroup.

The overall survival rate of frozen embryos after thawing was 93.86% with 95% confidence interval (CI) = 92.24–95.17%. Among cleavage stage embryos and blastocyst, the blastocyst showed lowest survival rate (∼94% vs 62.62%). The overall pregnancy rate was 52.03% (95% CI = 47.40–56.64%). Pregnancy rate was remarkably low in 2 cell stage FET group and was highest in blastocyst group (70.37%, 95% CI = 49.66–85.50%). The study yield that the biochemical pregnancy was lowest in blastocyst group (3.70%) and highest in 2 cell stage group (12.50%). The overall implantation rate was 22.79% (95% CI = 20.30–25.49%). The study showed the implantation of blastocyst was better than any other cleavage stage embryos following FET cycle. The overall clinical and ongoing pregnancy of the study population were 43.25% (95% CI = 38.73–47.90%) and 37.26% (95% CI = 32.89%–41.84%), respectively (Table −1).

Table 1.

Outcome of FET of study population.

Nomenclature	2 cell stage	4 cell stage	8 cell stage	Blastocyst	Overall
Survival rate N/N, % (95% CI)	46/50 92% (79.89–97.41)	611/631 96.83% (95.06–98.00)	341/362 94.20% (91.13–96.27)	42/65 64.62% (51.69–75.79)	1040/1108 93.86% (92.24–95.17)
Pregnancy rate N/N % (95% CI)	11/24 45.83% (26.17–66.76)	135/273 49.45% (43.39–55.53)	78/143 54.54% (46.03–62.82)	19/27 70.37% (49.66–85.50)	243/467 52.03% (47.40–56.64)
Biochemical pregnancy rate N/N % (95% CI)	3/24 12.50% (3.29–33.46)	18/273 6.59% (4.07–10.40)	19/143 13.29% (8.39–20.22)	1/27 3.70% (0.20–20.89)	41/467 8.78% (6.45–11.81)
Implantation rate N/N, % (95% CI)	9/46 19.57% (9.86–34.38)	137/611 22.42% (19.22–25.98)	71/341 20.82% (16.71–25.60)	20/42 47.62% (32.29–63.38)	237/1040 22.79% (20.30–25.49%)
Clinical pregnancy rate N/N, % (95% CI)	8/24 37.50 (19.55–59.24)	117/273 49.45 (43.39–55.53)	59/143 41.26% (33.19–49.80)	18/27 66.67% (46.01–82.76)	202/467 43.25% 38.73–47.90)
Ongoing pregnancy rate N/N, % (95% CI)	6/24 25.00% (10.60–47.05)	104/273 38.10% (32.36–44.17)	49/143 34.27% (26.67–42.72)	15/27 55.56% (35.64–73.96)	174/467 37.26% (32.89–41.84)
Ectopic pregnancy rate N/N, % (95% CI)	1/8 12.5% (0.66–53.32)	4/117 3.41% (1.10–9.04)	3/59 5.08% (1.32–15.05)	0/18 0% (0–21.88)	8/202 3.96 (1.85–7.94)
Miscarriage rate N/N, % (95% CI)	1/8 12.5% (0.66–53.32)	9/117 7.69% (3.80–14.50)	7/59 11.86% (5.30–23.54)	3/18 16.67% (4.41–42.27)	20/202 9.90% (6.30–15.08)
Multiple pregnancy rate N/N % (95% CI)	1/8 12.5% (0.66–53.32)	18/117 15.38 (9.62–23.49)	10/59 16.95% (8.86–29.42)	2/18 11.11% (1.94–36.07)	31/202 15.34% (10.82–21.23)

CI, confidence interval; FET, frozen thawed embryo transfer.

The study showed the first trimester adverse pregnancy outcome in form of ectopic pregnancy, miscarriage rate, and multiple pregnancy rate and were 3.96% with 95% CI = 1.85–7.94%, 9.90% with 95% CI = 6.30–15.08%, and 15.34% with 95% CI = 10.82–21.23%, respectively. There was no ectopic pregnancy noticed in blastocyst group of FET cycle, but miscarriage rate was higher than other cleavage stage FET subgroup (16.67% vs 8–12.5%).

Discussion

Age of the patient is one of the important factors which influences pregnancy. In our study, we found the mean age of the patient was 27.97 ± 2.672 yrs with range from 21 to 38 yrs. The study by Li et al. showed the mean age of study population as 29.9 ± 9.6 yrs with ranges between 21 and 43 years.⁴ Wang et al. showed the mean age 33.5 yrs, range 19–46.⁸ Yeung et al. reported the mean age = 36 yrs; SD = 4; and range = 22–45 yrs.⁹ In present study, the mean age of the population is relatively less because the age of marriage in India is less.

The overall survival rate of embryo thawing was 93.86% with 95% CI = 92.24–95.17%. Use of sequential culture media has been helped to develop approximately half of zygotes to blastocyst stage as it fulfilled the change in nutrient requirements of growing embryos on day to day basic.¹⁰ With utilization of the modern technology, we have achieved the survival rate of blastocyst 64.62%. Wang et al. reported the embryo survival rate of 69% after thawing of cryopreserved embryos.⁸ Wang et al. in 2012 reported the survival rate of 88.5%.¹¹ Han et al. also reported 93.3% survival after thawing.¹²

In our study, we found the pregnancy and clinical pregnancy rate of blastocyst transfer were 70.37% and 66.67%, respectively. The pregnancy outcome in blastocyst was better than other cleavage stage embryo transfer. Glujovsky et al. in one of Cochrane Database of Systematic Reviews reported the increased incidence of clinical pregnancy rate in blastocyst group by approximately 3–10% from cleavage stage groups.¹³ In present study, we found the difference of 25.41–29.17% in clinical pregnancy rate between blastocyst group of FET and different cleavage cell of FET (Table −1). This difference was probably because of association of overall increased rate of clinical pregnancy in FET cycle. This difference in pregnancy outcome is also supported Cochrane Database of Systemic Reviews by Wong et al.¹⁴ This review found the overall clinical pregnancy rate in blastocyst group was ranged from 56 to 65%.¹⁴ The overall clinical pregnancy rate was 43.25% across all group, and it was consistent with the finding of other published studies by Salumets et al.¹⁵ and Veleva et al.¹⁶

During the study, we found the overall ectopic pregnancy rate, miscarriage rate, and multiple pregnancy rate were 3.96%, 9.90%, and 15.34%, respectively. Chen et al. reported the ectopic pregnancy rate of 4.3%.¹⁷ Xu et al. reported miscarriage rate of 16.4%.¹⁸ Yeung et al. in their study reported multiple pregnancy rate of 18%.⁹ In our study, we found no ectopic pregnancy in blastocyst transfer group, whereas 2 cell stage transfer was associated with higher ectopic pregnancy rate (approximately 12.5%). This was another advantage of preferring blastocyst transfer during FET.

Conclusion

The cryopreservation of embryo and FET has now become an accepted procedure of ART since its success from 1983. FET provides another chance to patient undergo embryo transfer (ET) and contributes to achieve higher cumulative pregnancy rate. The present study results have indicated the overall survival rate of 90% in case of cleavage embryos and blastocyst had survival rate of 65%. From the result observed in the present study, we have found implantation and clinical pregnancy and ongoing pregnancy rate were better among blastocyst than other type of cleavage cell stage embryo transfer. The adverse first trimester pregnancy outcome inform of miscarriage, ectopic, and multiple pregnancy did not show significant difference for different cell stages and blastocyst FET. Observing the result of present study, we conclude that where multiple embryos are available, these should be cultured to blastocyst stage, cryopreserved, and then to be used for frozen thawed blastocyst transfer for better implantation and ongoing pregnancy.

Conflicts of interest

The authors have none to declare.