WEDNESDAY, Nov. 13 (HealthDay News) -- Babies born to women who've had weight-loss surgery are more likely to be premature and to have low birth weights, a new study found.
These pregnancies should be considered at-risk and require careful monitoring by doctors, said the researchers at the Karolinska Institute, in Sweden.
The investigators compared more than 2,500 babies born between 1992 and 2009 to women who'd had weight-loss surgery with a comparison group of 12,500 babies born to women who had not had this type of procedure, known as "bariatric" surgery.
The analysis revealed that 5.2 percent of infants born to women who'd had weight-loss surgery were small for gestational age and 4.2 percent were large for gestational age. This compared to 3 percent and 7.3 percent, respectively, of those infants whose mothers had not had the surgery.
The researchers also found that 9.7 percent of the infants born to mothers who'd had weight-loss surgery arrived prematurely (before 37 weeks), compared with 6.1 percent of other infants.
No differences were seen between the two groups in rates of stillbirth or death within the first 27 days after birth, according to the study published online Nov. 12 in the journal BMJ.
Although the study found an association between women having weight-loss surgery and higher risk of pregnancy with prematurity or lower birth weight, it did not establish a cause-and-effect relationship.
"The mechanism behind how [weight-loss] surgery influences fetal growth we don't yet know, but we do know that people who have bariatric surgery are at increased risk of micronutrient deficiencies," Dr. Olof Stephansson, an obstetrician and associate professor at the clinical epidemiology unit at Karolinska, said in an institute news release.
The researchers noted that an increasing number of people are having weight-loss surgery and said that the pregnancies of women who've had the surgery should be considered at-risk and require particularly close attention. For example, they should have extra ultrasounds to check fetal growth or be given special dietary supplement recommendations.
But the study authors also pointed out that weight-loss surgery has numerous benefits for mothers, such as reducing the risk of diabetes, heart disease, cancer and stroke. In addition, obesity is a known risk factor for both mother and baby during pregnancy and childbirth.
The March of Dimes has more about pregnancy after weight-loss surgery.