Researchers found there are both pros and cons to bariatric surgery before pregnancy.

Pregnant women who are obese are more likely to develop complications during pregnancy and after birth, but bariatric surgery was linked to an increased rate of babies who were too small for their gestational age, the Karolinska Institutet reported.

"The effects of bariatric surgery on health outcomes such as diabetes and cardiovascular disease have been studied, but less is known about the effects on pregnancy and perinatal outcomes," said the study's lead author, Kari Johansson, from the Department of Medicine. "Therefore we wanted to investigate if the surgery influenced in any way the risk of gestational diabetes, preterm birth, stillbirth, if the baby was small or large for its gestational age, congenital malformations and neonatal death."

To make their findings, the researchers looked at 596 pregnancies in women who had already received bariatric surgery between 2006 and 2011 as well as 2,356 pregnancies in women who had not received the surgery but had the same body mass index as the first group did before the procedure.

The findings revealed women who had undergone surgery had a reduced risk of developing gestational diabetes (a drop from 7 percent to 2 percent). Over 22 percent of women in the comparison group had babies that were larger than average, compared with 9 percent of the operated women. Women who had undergone the surgery were twice as likely to give birth to babies who were small for gestational age and tended to have shorter pregnancies.

"Since bariatric surgery followed by pregnancy has both positive and negative effects, these women, when expecting, should be regarded as risk pregnancies," Johansson said. "They ought to be given special care from the maternal health services, such as extra ultrasound scans to monitor fetal growth, detailed dietary advice that includes checking the intake of the necessary post-surgery supplements."

The findings were published in a recent edition of the New England Journal of Medicine.