Insufficient Implementation of Recommendations in Pregnancies after Bariatric Surgery: Results from a Nationwide Real-World Study in Germany (PABS Study)

Abstract

Introduction Bariatric metabolic surgery (MBS) is increasingly performed in women of reproductive age. Although MBS reduces obesity-related pregnancy complications, altered metabolism and nutritional deficiencies may adversely affect maternal and neonatal outcomes. This study evaluated (1) adherence to current guideline recommendations and (2) pregnancy outcomes in women after MBS in Germany.

Materials and Methods In this multicenter cohort study, 410 pregnancies after MBS were collected between 2023 – 2025; 380 cases with complete data on BMI, MBS type, and birth weight were finally analyzed. Maternal characteristics, surgical details, preconceptional and prenatal care, and perinatal outcomes were descriptively assessed and compared with national reference data.

Results Preconceptional BMI was 30.1 kg/m ² , 52% of the women were obese. Most common procedures were Roux-en-Y gastric bypass (RYGB; 58%) and sleeve gastrectomy (38%). Overall, 16% of the women conceived < 1 year after MBS, 27% after 1 – 2 years, and 57% after > 2 years. Before conception, 35% of the women neither received supplementation nor assessment for deficiencies (52%); similar rates were observed during pregnancy. Anemia occurred in 40%, particularly after RYGB. Oral glucose tolerance testing for gestational diabetes screening was used in 33% despite recommendations against it after MBS. Gestational diabetes was diagnosed in 23%. Rates of small and large for gestational age newborns were 20% and 6%, respectively; preterm birth occurred in 10% and C-section in 46%.

Conclusions High rates of anemia and SGA highlight the need for specialized high-risk pregnancy care after MBS. Several guideline recommendations regarding surgery-to-conception interval, supplementation, and GDM screening were not consistently followed.

Introduction

Bariatric metabolic surgery (MBS) has emerged as an effective intervention for severe obesity and its related comorbidities, with substantial short- and long-term health benefits. As the prevalence of obesity continues to rise globally, more women of reproductive age undergo bariatric surgery procedures. According to the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO) global registry, 81% of bariatric surgeries worldwide are performed on women. Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) are the most performed procedures 1 . Pregnancy after MBS presents a unique clinical scenario characterized by altered nutritional status and potential deficiencies and surgical-related sequelae, which can influence both maternal and fetal outcomes. MBS is supposed to reduce obesity related fertility and pregnancy complications 2 ,  3 such as early pregnancy loss, gestational diabetes mellitus (GDM), excessive fetal growth, hypertensive disorders, cesarean deliveries, preterm births, and stillbirths. On the other hand, new challenges in pregnancy care arise that may lead to an adverse outcome. Increased demand for nutrients during pregnancy may not be met due to decreased absorption of nutrients 4 . Deficiency of maternal micronutrients are highly prevalent during pregnancy after MBS 5 , low maternal concentrations of vitamins A, B ₁₂ , and D, folic acid, iron, and zinc occur frequently 6 . An increasing risk of prematurity and small-for-gestational-age (SGA) babies have been reported 7 ,  8 ,  9 . The etiopathogenesis of these adverse effects remains largely unknown.

Taking care of pregnant women after MBS remains a new challenge for caregivers, and general knowledge is not yet widespread. In Germany, national guidelines for antenatal care after MBS were established in 2019 as a section of the AWMF guideline on obesity and pregnancy 10 , drawing on Shawe et al. 11 and other published recommendations 12 ,  13 , to optimize care in this population. Key recommendations include an interval of at least one year between surgery and conception to avoid pregnancy during the rapid weight-loss phase, tailored nutritional supplements, and regular evaluation to assess potential deficiencies before and during pregnancy. Additional measures include testing for GDM using venous fasting glucose, HbA1c, and glucose profiles instead of oral glucose tolerance tests, as well as sequential fetal biometry for early detection of fetal growth restriction.

The aim of this study was to evaluate the extent to which current guidelines are implemented in clinical practice by healthcare providers and adhered to by women, with particular focus on the surgery-to-conception interval, supplementation, micronutrient assessment, and GDM screening. Secondarily, we assessed maternal and fetal outcomes in pregnancies following MBS in our study population.

To address this, we conducted a nationwide multicenter study in Germany to obtain a comprehensive overview of the current care situation ( P regnancy A fter B ariatric S urgery = PABS Study).

Materials and Methods

Cohort composition

Data of pregnancies in women after MBS had been prospectively and retrospectively collected in 13 delivery units (see Supplement Table S1 ) between 01/2023 and 12/2025 using a standardized Case Report Form (CRF) (see supplements). This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the “Ärztekammer Berlin” (14.12.2022/Eth-37/20). Waiver for informed consent was approved if deduction of the patientʼs identity out of the anonymized data could be ruled out. All hospitals were advised to obtain informed consent.

Clinical variables and perinatal outcomes

Data were retrieved from patient records and included maternal baseline characteristics, medical history with particular focus on metabolic and bariatric surgery (MBS), pregnancy course, and perinatal outcomes.

MBS-related data comprised type of surgery, date of operation (month and year), maternal body mass index (BMI in kg/m ² ) at the time of surgery, and weight loss until conception, expressed as absolute weight loss (kg) and percentage of total body weight loss (%TBWL). In addition, information on the intake of tailored micronutrient supplementation after MBS and documented nutritional deficiencies prior to pregnancy was collected. Preconceptional comorbidities, including preexisting diabetes, chronic hypertension, and anemia, were also recorded. The interval between MBS and conception was categorized as < 1 year, 1 – 2 years, and ≥ 2 years.

Pregnancy-related data included gestational weight gain (GWG) from conception until delivery (kg), categorized according to the National Academy of Medicine (NAM) recommendations 10 . Perinatal complications, including intrauterine fetal demise and hypertensive disorders of pregnancy, as well as GDM, were documented. GDM data were analyzed in greater detail, including the type of diagnostic testing and test leading to the diagnosis. GDM diagnostic was based on “The International Association of the Diabetes and Pregnancy Study Groups” (IADPSG) criteria according to national guidelines 10 .

Obstetric and delivery data were obtained from patient records. Neonates were classified as small for gestational age (SGA) if birth weight was below the 10th percentile and as large for gestational age (LGA) if birth weight exceeded the 90th percentile according to contemporary sex-specific German growth charts 14 . Preterm birth was defined as delivery before 37 weeks of gestation and very preterm birth as delivery before 34 weeks.

Only cases with complete data on maternal pre-pregnancy BMI, type of MBS, and neonatal birth weight categories were included in the final analysis.

Comparison cohort

Our results were compared with nationwide obstetric data from the 2024 federal quality report published by the Institut für Qualitätssicherung und Transparenz im Gesundheitswesen (IQTIG) 15 .

Statistical methods

Categorical variables are presented as absolute numbers and percentages and were compared using the two-sided χ ² test. Continuous variables are reported as median and interquartile range (Q1–Q3). Normality of distribution was assessed using the Shapiro–Wilk test. As most variables were not normally distributed, comparisons between two groups were performed using the Mann–Whitney U test and between more than two groups using the Kruskal–Wallis test. The level of statistical significance was set at α = 0.05. Due to the exploratory nature of the study, no adjustment for multiple testing was applied. Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS), version 30.0 (IBM Corp., Armonk, NY, USA).

Results

Description of the cohort

A total of 410 cases were available. Cases with missing data on BMI, method of MBS, birth weight percentiles analyzed and twins were excluded from analysis, leaving 380 cases for analysis ( Fig. 1 ). The extent of missing data for the other parameters is presented in Tables 1 and 2 . Maternal characteristics are shown in Table 1 . Median BMI was still 30.1 kg/m ² (IQR 27 – 35.2); 52.4% of the women were classified as obese and 7.5% had preexisting diabetes mellitus and 5.3% preexistent hypertension.

Fig. 1.

 Composition of the PABS cohort included in the present analysis. A total of 410 pregnancies after metabolic bariatric surgery (MBS) were available for assessment. Cases with missing data on body mass index (BMI), type of MBS, or birth weight percentiles, as well as twin pregnancies, were excluded, leaving 380 singleton pregnancies for final analysis. PABS, pregnancy after bariatric surgery; n, number of cases; BMI, body mass index; MBS, metabolic bariatric surgery; RYGB, Roux-en-Y gastric bypass.

Table 1  Preconceptional characteristics of total cohort (n = 380).

Variables	Available data
Data are presented as median (Q1–Q3) or frequency (percentage). Due to missing data, the number of available observations differed between variables. BMI, body mass index; MBS, metabolic bariatric surgery; RYGB, Roux-en-Y gastric bypass; SG, sleeve gastrectomy; GB, gastric banding; TBWL, Total Body Weight Loss
Maternal age (years)	380	33 (29 – 36)
Parity	370	2 (1 – 3)
Prepregnancy maternal weight (kg)	380	85.2 (73 – 98)
Prepregnancy BMI (kg/m 2 )	380	30.1 (27 – 35.2)
Obesity (BMI > 30 kg/m 2 ) (%)	380	199 (52.4)
Comorbidities (%)	375
Preexistent hypertension		20 (5.3)
Preexistent diabetes mellitus		28 (7.5)
MBS – Mode of surgery (%)	380
RYGB		219 (57.6)
SG		142 (37.5)
GB		19 (5)
Maternal BMI before MBS (kg/m 2 )	312	46 (41.7 – 52)
Weight loss from surgery to conception (kg)	312	48 (37 – 60)
TBWL from surgery to conception (%)	312	36 (29 – 44)
Interval surgery to conception (%)
< 1 year	375	59 (15.7)
1 – 2 years		102 (27.2)
> 2 years		214 (57.1)
Preconceptional supplement intake (%)	373	244 (65.4)
Preconceptional micronutrient monitoring (%)	371	178 (48)

Table 2  Pregnancy and neonatal outcomes of total cohort (n = 380).

Variables	Available data
Data are presented as median (Q1–Q3) or frequency (percentage). Due to missing data, the number of available observations differed between variables. NAM, National Academy of Medicine; GDM, gestational diabetes mellitus; AGA, appropriate-for-gestational-age (10 – 90th percentile); LGA, large-for-gestational-age (≥ 90th perc.); SGA, small-for-gestational-age (< 10th percentile); GA, gestational age; GWG, gestational weight gain; NICU, neonatal intensive care unit; HPD, Hypertensive disorders of pregnancy; IUFD, intrauterine fetal demise
Micronutrient monitoring	369
Never		132 (35.8)
Once during pregnancy		104 (28.2)
Every 3 month		133 (36.0)
Supplement intake (%)	366
No		120 (32.8)
Yes		246 (67.2)
Beginning of supplement intake	246
Start 1st trimester		228 (92.6)
Start 2nd trimester		9 (3.7)
Start 3rd trimester		9 (3.7)
GWG (kg)	351	11 (6 – 16)
Adherence to NAM recommendations
Inadequate		97 (27.6)
Adequate		71 (20.2)
Excessive		183 (52.1)
GWG according to surgery-to-conception interval (kg)	346
< 1 year	52	6 (0.6 – 14.3)
1 – 2 years	96	11.5 (7 – 15.8)
> 2 years	198	12 (8 – 17)
Anaemia	376	149 (39.6)
Oral therapy		74 (49.7)
i. v. therapy		75 (50.3)
IUFD	378	2 (0.5)
HPD	377	15 (3.8)
GDM	364	82 (22.5)
GA at delivery (weeks)	376	39 (38 – 40)
Preterm delivery < 37 weeks	376	23 (6.1)
Preterm delivery < 34 weeks	376	14 (3.7)
Mode of delivery	379
Vaginal birth		193 (50.9)
Assisted vaginal birth (vacuum or forceps)		12 (3.2)
Planned C-section		110 (29)
Emergency C-section		64 (16.8)
Birth weight percentile	380
SGA		76 (20)
AGA		282 (74.2)
LGA		22 (5.8)
NICU admission	371	50 (13.5)

Timing of pregnancy and gestational weight gain

The majority underwent Roux-en-Y gastric bypass (RYGB) (57.6%) as MBS procedure and most pregnancies occurred more than two years after surgery (57.1%) ( Table 1 ). However, ~ 16% became pregnant within the first year after surgery. Gestational weight gain (GWG) had a wide range (median 11 kg, IQR 6 – 16) with one in four women gaining less than the amount recommended by the National Academy of Medicine (NAM) 16 ( Table 2 ). GWG did not differ between women with different MBS methods. However, there was a significant association of GWG and interval since surgery: women who became pregnant within the first year after MBS gained 6 kg (0.6 – 14.3), those with an interval of 1 – 2 years 11.5 kg (7 – 15.8) and more than 2 years 12 kg (8 – 17) (p < 0.001). A total of 25 (7.1%) women lost weight during pregnancy with the highest proportion observed in those who conceived less than one year after surgery compared to longer intervals of 1 – 2 years or more than 2 years (23.1% vs. 8.3% vs. 2.5% for < 1 year, 1 – 2 years and > 2 years, respectively, p < 0.01) (data not shown).

Supplementation status and maternal anemia

Supplements were taken preconceptionally by 65.4% of the women and nutritional deficiencies were assessed in 48% of cases ( Table 1 ). The rate of supplement intake decreased significantly with increasing surgery-to-conception interval. Reported supplement use was 74.6% among women who conceived within 1 year after surgery, 75.0% among those who conceived 1 – 2 years after surgery, and 58.1% among those who conceived more than 2 years after surgery (p = 0.004; data not shown). During pregnancy ( Table 2 ), the percentage of supplement intake was similar (67.2%), with a slightly higher rate of deficiency assessment (64.2%). Anemia was frequently observed (39.6%), with the highest rate reported when surgery-to-conception interval exceeded two years (45%) (p = 0.04). 50.3% of the women required intravenous iron supplementation, which was significantly more frequent in women with RYGB than in those with SG or GB (25.1% vs. 14.1% vs. 0%, p = 0.002 respectively) ( Table 3 ).

Table 3  Anaemia rates and treatment requirements according to type of metabolic bariatric surgery (n = 376; p = 0.002).

Variables	All	GB	SG	RYGB
Data are presented as frequency (percentage). RYGB, Roux-en-Y gastric bypass; SG, sleeve gastrectomy; GB, gastric banding
No anaemia	227 (60.4)	18 (94.7)	93 (65.5)	116 (54)
Oral Iron supplementation	74 (19.7)	1 (5.3)	29 (20.4)	45 (20.9)
I. v. iron supplementation	75 (19.9)	0	20 (14.1)	54 (25.1)

GDM and diagnostics

The rate of GDM was more than twice as high as in the general population (22.5% vs. 10.3%): 82 out of 364 women with available data 14 . Screening for GDM was performed using either a 50 g glucose challenge test (GCT) and/or a 75 g oral glucose tolerance test (oGTT) in 32.6% of women, followed by glucose profiles (22.4%), venous fasting glucose measurements (14.9%), and HbA1c testing (5%). Notably, 25.1% of women did not receive any GDM diagnostic assessment. A diagnosis of GDM was documented in 22.5% of women, with cases distributed almost equally among those diagnosed by 75 g oGTT (31.7%), glucose profiles (40.2%), and fasting glucose measurements (28%) ( Table 4 ).

Table 4  Gestational diabetes mellitus (GDM) diagnostics performed during pregnancy (n = 380), including initial screening methods, number of GDM diagnoses, and final diagnostic modality used for GDM confirmation.

Variables	Available data
Data are presented as frequency (percentage). Due to missing data, the number of available observations differed between variables. GDM, gestational diabetes mellitus; GCT, glucose challenge test; oGTT, oral glucose tolerance test
GDM testing methods	362
50 g GCT and/or 75 g oGTT		118 (32.6)
Glucose profiles		81 (22.4)
Fasting glucose		54 (14.9)
HbA1c		18 (5.0)
None performed		91 (25.1)
GDM diagnosis	364	82 (22.5)
GDM diagnosis based on	82
Glucose profiles		33 (40.2)
75 g oGTT		26 (31.7)
Fasting glucose		23 (28)

Perinatal outcome

Newborns were delivered more frequently preterm (6.1 vs. 4.9%), with a particular high rate of very preterm deliveries (3.7 vs. 1.7%), and more often by C-section (45.8% vs. 34.1%) compared to the general German population in 2024 15 . The rate of infants born SGA was notably high (20% vs. 9.3%), whereas the rate of LGA infants was comparatively low (5.8% vs. 9.8%). Overall, 13.5% of newborns required transfer to the Neonatal Intensive Care Unit (NICU) ( Table 2 ).

Discussion

Summary of results

The rate of obstetrical complications was higher than in the general population. These included inadequate gestational weight gain (GWG) as well as increased incidences of GDM, preterm birth, SGA neonates and cesarean delivery. Implementation of national recommendations for preconceptional and prenatal care after MBS was insufficient. First, supplementation and assessment of nutritional deficiencies were reported in only about 50 – 60% of women. Second, 15.7% of the women did not adhere to the recommended minimum surgery-to-conception interval. Third, despite clear guideline recommendations to avoid oral glucose tolerance testing after MBS because of the risk of adverse events such as dumping syndrome, reactive hypoglycemia, and inaccurate glucose measurements, 32.6% of women underwent either a 50 g GCT or a 75 g oGTT. Finally, almost 27.6% of women gained less weight during pregnancy than recommended based on their pre-pregnancy BMI.

Comparison with literature

Women with obesity generally tend to deliver infants with higher birth weights. In contrast, 20% of the newborns in our cohort were classified as SGA, despite more than 50% of the women being obese. Previous studies have consistently reported increased rates of SGA infants after MBS, comparable to those observed in our cohort 8 ,  9 . The pathophysiological mechanisms underlying restricted fetal growth following MBS, as well as the reported increased rates of preterm delivery, remain incompletely understood 17 . In our cohort, 6.1% of newborns were delivered before 37 weeks of gestation, compared with 4.9% in the general population. However, descriptive comparison with nationwide reference data should be interpreted with caution. Of particular concern is the markedly elevated incidence of very preterm birth, which was 3.7% in our cohort – almost twice the rate reported for the German population in 2024 15 . While preterm delivery between 34 – 37 weeks may partly be iatrogenic due to suspected fetal compromise associated with fetal growth restriction, this explanation is unlikely for very preterm delivery. The high prevalence of both SGA and very preterm deliveries in our cohort may also partly explain the elevated C-section rate of 45.8%. Overall, pregnancies following MBS should be considered high-risk pregnancies and therefore require close obstetric surveillance.

Pregnant women with a history of MBS are at high risk of developing nutrient deficiencies 18 . A significant proportion of these women neither adhere to intake of recommended supplementation nor undergo appropriate assessment of micronutrient status before or during pregnancy 19 . Non-compliance tends to increase with longer intervals since surgery, however, even amongst women who conceived within the first postoperative year, 35% reported not taking supplement specifically formulated for post-MBS patients. The most frequently cited reasons were lack of information regarding the necessity of lifelong supplementation to meet nutritional requirements, followed by general non-compliance, limited financial resources and in some cases, recommendations from health care providers to discontinue supplementation after conception due to concerns about potential teratogenic effects of high vitamin A levels 19 . Inadequate post-surgical care was pronounced amongst women who underwent surgery outside the German healthcare system. Although annual screening of nutritional deficiencies after MSB is officially covered by health insurance, many women reported that health care providers often required them to cover the costs themselves. Furthermore, essential supplements such as multivitamins, vitamin D and vitamin B ₁₂ are not reimbursed, despite their crucial role in preventing post-surgical complications – comparable to routine coverage of medications for other deficiency-related conditions, such as hypothyroidism.

Anaemia is a common complication after MBS and is further exacerbated by the increased iron demand during pregnancy. In our study up to 45% of the women were affected by anaemia, with iron deficiency frequently necessitating intravenous supplementation for effective management.

Women following MBS often remain overweight or obese, as reflected in our cohort, in which more than 50% were classified obese. GWG in these pregnancies is often inadequate, most commonly due to excessive GWG compared to NAM recommendations, with reported rates up to 48% in other studies 20 which is comparable to the 52% in our cohort. Insufficient GWG with 27.6% of the women gaining less than recommended weight during pregnancy was comparable with the presented percentages in a meta-analysis as well, ranging from 15 to 39 percent 20 . Low GWG was particularly common among women who conceived within the first year after surgery.

The association between amount of GWG and between surgery-to-conception interval has been described previously 21 , with some evidence suggesting that longer intervals may be associated with excessive GWG. Despite the differences in the extent of intestinal malabsorption depending on the surgical procedure, GWG did not significantly differ by type of bariatric procedure in our cohort. This is in line with smaller studies with sample sizes around 90 or 100 cases 22 ,  23 which similarly reported no differences in GWG according to surgical technique.

The observed GDM prevalence of 22.5% remains higher than in the general obstetric population (9.4%), likely reflecting the persistently elevated BMI and insulin resistance. Comparable rates have been reported in other studies 8 . However, the true prevalence of GDM after MBS remains uncertain due to the lack of standardized diagnostic criteria and heterogeneity in screening approaches. Given the limited accuracy and poor tolerability of the oGTT following MBS, there is broad consensus that neither the 75 g oGTT nor the 50 g GCT should be used for GDM screening after MBS. Standard diagnostic criteria cannot be reliably applied due to altered glucose absorption 24 . Performing a 50 g GCT or 75 g oGTT may even expose patients to adverse effects. Altered gastrointestinal glucose transit after surgery results in rapid postprandial glucose excursions followed by reactive hypoglycemia and dumping syndrome, particularly after high carbohydrate intake. Nevertheless, guideline recommendations were not consistently followed, and approximately one third of women in our cohort underwent an oGTT. There is also no consensus regarding optimal management of GDM in this population. Glycemic variability during pregnancy appears to differ according to the type of bariatric procedure performed 25 . Given the relatively low incidence of pre-eclampsia and large-for-gestational-age (LGA) neonates observed after MBS, the benefit of pharmacological treatment for mild hyperglycemia remains unclear 26 .

Strengths and limitations

This study has several strengths. The multicenter design and inclusion of data from centers across Germany provide a broad overview of the current management of pregnancies following MBS and enhance the representativeness of the findings. However, several limitations should be considered. First, the registry captures only a proportion of pregnancies after MBS in Germany and may therefore not fully reflect the national population. Second, fetal growth assessment was based on Voigt percentiles 14 and recorded only as categorical data, which limited the possibility of analyzing birth weight as a continuous variable. Third, information on maternal ethnicity was not available, although ethnic background is known to influence fetal growth patterns. Fourth, maternal and neonatal data was not completely available in all cases as shown in the tables. Missing data was not imputed. Analyses were performed based on available cases for each variable; therefore, denominators may vary between analyses and tables. In addition, potential language barriers, which may affect patient counselling, adherence to supplementation, and access to care, were not captured in the dataset. Finally, as this study is based on registry data, the retrospective design limits the ability to assess causal relationships.

Despite these limitations, the study provides valuable insight into the current clinical management of pregnancies following MBS and highlights relevant gaps in guideline implementation.

Conclusion

This registry-based cohort study suggests relevant gaps in the clinical management of pregnancies following MBS. Low rates of micronutrient supplementation and deficiency assessment, conception within a short interval after surgery, and the continued use of oral glucose tolerance tests for GDM screening indicate inconsistent implementation of current recommendations in clinical practice. These findings underline the importance of specialized preconceptional and prenatal care for women after MBS. Increased awareness among healthcare professionals and structured counselling before and during pregnancy may help to improve adherence to guideline recommendations and maternal nutritional care in this high-risk population.