When Is the Ideal Time to Try for a Baby After Bariatric Surgery?

Becky McCall

May 12, 2022

Doctors are advising women who have had bariatric surgery to wait at least 2 years before trying to conceive to reduce the risk of a small-for-gestational-age baby.

In fact, babies conceived less than 2 years post-bariatric surgery are 15-times more likely to be small for gestational age as those conceived after this cut-off point, new study findings indicate.

Ana Carreira, MD, Coimbra Hospital and University Centre, Portugal, presented the findings as a poster at the European Congress on Obesity (ECO) 2022.

"The prevalence of small-for-gestational-age babies was similar across the different types of bariatric surgery, and we calculated that the cut-off for the bariatric-surgery-to-conception interval for a lower risk of small for gestational age babies was 24.5 months," Carreira reported.

The study also found that for each additional month after the 2-year time point from bariatric surgery to conception, there was a 4.2-g (0.15-oz) increase in birth weight and there was a 5% lower risk for a small-for-gestational-age neonate. 

"Clinically, this is very significant," she told Medscape Medical News.

"While it may be possible to slightly adjust this on an individual basis, it is important that women who are undergoing bariatric surgery are aware of the risk of early conception and of the benefits of delaying pregnancy," she added.

Asked to comment, Kari Johansson, PhD, of the Karolinska Institute, Stockholm, Sweden, who has worked in the field, said: "These increased risks have been hypothesized to potentially be attributed to the inadequate in utero availability of nutrients to the fetus, especially during the first year post-bariatric surgery when the rapid and largest weight loss occurs. This is why many clinical guidelines recommend women wait 12-24 months until getting pregnant."

Indeed, the American College of Obstetricians and Gynecologists recommends women wait 12-24 months post-bariatric surgery before trying to conceive.

Johansson also noted, however, that there were no significant increased risks of adverse outcomes between pregnancies with a surgery-to-conception interval of 12 months or less versus over 12 months in a recent meta-analysis. But those authors also concluded that large cohorts with sufficient power are needed "before any definite conclusions can be made on the optimal surgery-to-conception interval," she cautioned.

All Types of Bariatric Surgery Investigated

Bariatric surgery, which is increasingly popular in women of reproductive age, involves rapid weight loss, which can trigger improved fertility, Carreira explained. Currently, clinics generally advise women to wait at least 1 year before trying for a baby post-surgery.

Carreira and colleagues conducted the study because "the optimal bariatric-surgery-to-conception interval has yet to be determined" and they wanted to examine the issue of small-for-gestational-age babies in particular, she noted. They also examined outcomes after a number of different bariatric procedures.

They retrospectively reviewed a cohort of 48 post-surgery pregnancies (in 2008-2020) with a minimum follow-up of 30 weeks and determined the proportion of small-for-gestational-age neonates, defined as having a birth weight less than the 10th percentile according to National Center for Health Statistics growth charts.

Mean maternal age was 34.3 years, mean body mass index (BMI) at conception was 30.9 kg/m2, and 70.8% had a bariatric-surgery-to-conception interval of over 24 months, 14.6% of 12-24 months, and 14.6% of less than 12 months.

Bariatric surgeries included adjustable gastric banding (22.9%), sleeve gastrectomy (35.4%), Roux-en-Y gastric bypass (37.5%), and biliopancreatic diversion (4.2%).

Overall, mean birth weight was 2.98 kg (6.6 lb) and the prevalence of small-for-gestational-age babies was 26.3%.

"For an interval of less than 24 months, around 60% of babies were small for gestational age," Carreira noted. 

Most babies who were small for gestational age were conceived at 18 months (median), and those who were not were conceived at 59 months (median).

And, after adjustment for maternal comorbidities, the odds ratio for a small-for-gestational-age neonate was 15.1 (95% CI, 2.4 - 93.1) for a baby conceived less than 24 months after surgery.  

"Some people think the interval can change according to the type of bariatric surgery, but we found no difference in findings according to [surgery] type," added Carreira.

She pointed out that after discharge from their endocrinology clinic (after bariatric surgery), the women are cared for by their family doctor, "and we find that when they return to us in pregnancy their nutrient deficiencies have not been properly addressed. They need to be addressed at least 6 months prior to conception."

"We recommend that women wait at least 2 years after bariatric surgery before trying to conceive, irrespective of the type of surgery," she reiterated.

ECO 2022. May 3-7, 2022. Poster no. 4.73.

Carreira and Johansson have reported no relevant financial relationships.

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