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Surgery and pregnancy

Does gastric bypass impact foetal growth?

More studies are needed to assess maternal safety and neonatal outcomes in pregnancies conceived after surgery

Bariatric surgery could result in an increased risk of reduced foetal growth, according to researchers from Denmark. Although they acknowledge that their study found that there was no significant relation was found between the surgery-to-conception interval and early foetal growth or risk of small-for-gestational age (SGA). They concluded that “more studies are needed to provide information on maternal safety and neonatal outcomes in pregnancies conceived after bariatric surgery”.

In many countries the recommendations have been to postpone pregnancy to 12–18 months after surgery when weight loss generally has reached a plateau. Therefore, the researchers from Copenhagen University Hospital, Aarhus University Hospital, Ann Tabor Center of Fetal Medicine and Copenhagen University Hospital Rigshospitalet, wanted to examine the optimal timing of pregnancy after bariatric surgery as there is some concern that pregnancies conceived rapidly after surgery occur in a period of rapid weight loss which may theoretically cause foetal malnutrition.

In order to evaluate foetal growth in relation to the time interval between gastric bypass surgery and conception, they examined the national cohort data on women who had laparoscopic or open gastric bypass surgery prior to becoming pregnant. The main outcome measures were early and late foetal growth in relation to time from bariatric surgery to conception of the pregnancy.


The study identified 387 women who became pregnancy after gastric bypass surgery and were included in the study. Women in the study group had higher BMI than the general population of pregnant women (range 18–57). Maternal characteristics and lifestyle factors are presented in Table 1. The surgery-to-conception interval ranged from 3 to 1,851 days with a mean value of 502 days.

Table 1: Maternal characteristics of women with gastric bypass prior to their pregnancy compared to all pregnancies registered in the Danish Fetal Medicine Database in 2008

The overall proportion of newborns being SGA in the study group was 64/336 (19.0%) and the proportion of large-for-gestational age (SGA) newborns was 22/336 (6.5%). The proportion of SGA newborns in women with BMI less than 25 was 8/27 (29.6%), 23/117 (19.6%) in women with BMI 25–30 and 31/185 (16.8%) in women with BMI above 30, showing no significant difference (p=0.3).

The risk of LGA was 0/27 (0%), 5/117 (4.3%) and 17/185 (9.2%) in women with BMI below 25, between 25 and 30 and above 30, respectively, (p=0.09).

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