Obese women run the risk of problems during pregnancy, labour and complications for the baby's health. A new study of more than 3000 expectant mothers confirms this, and also reveals that being underweight also has specific complications.

Researchers at University Hospital Virgen de las Nieves, in Granada, have identified the risks in pregnancy related specifically to obesity and have compared them to underweight women to confirm that extreme slimness also carries a risk.

"During pregnancy, obesity is linked to hypertension, gestational diabetes, premature labour, macrosomy of the fetus and unexplained death during labour" Sebastián Manzanares, the first author of the study said. "Nonetheless, there is still little data about the link between being underweight and perinatal complications."

The study, which has been published in The Journal of Maternal-Fetal and Neonatal Medicine, includes a sample of 3,016 pregnant women, 168 (5.5%) with extreme slimness, 2,597 (86.1%) with a normal weight and 251 (8.3%) being seriously or morbidly obese.

The results show that obese mothers have a higher risk of developing hypertension, diabetes mellitus, and colonization with group B streptococcus. Also in these women it is more common to induce labour or undergo a caesarean section, whether elective or emergency. It is also more common for macrosomy or acidosis to occur at birth, or for the baby to die before it is born.

Furthermore, underweight women are more prone to oligohydramnios (reduction in the amount of amniotic liquid) and for their newborns to be underweight. The incidence of women going into labour prematurely or late did not differ significantly in relation to the mother's weight.

"Severely or morbidly obese mothers have a higher risk of adverse results and perinatal mortality, and therefore should be advised about weight loss and how to recognise the early warning signs of possible complications" Manzanares highlights. "Nonetheless, this group, as well as underweight women, should be considered "high risk."

Chubbier babies

The new study shows that newborns of severely or morbidly obese mothers are fatter. Furthermore, the risk of fetal macrosomy is 2.3 times greater in this group in comparison to women with a normal weight.

For the authors "these results justify the need of assessment before pregnancy and it could be a convincing argument for weight modification." "The study shows a higher risk in cases of severe or morbid obesity and also in underweight women" Manzanares concludes.