STOCKHOLM - Babies of overweight and obese mothers are more likely to have oxygen-deprivation problems at birth, according to a new study.
The heavier a woman is, the greater the risks to her newborn, researchers found.
"Maternal obesity is associated with a number of complications during pregnancy and delivery, but the underlying mechanism is not fully understood," said Dr. Marie Blomberg of Linkoping University in Sweden. She was not involved in the new study.
To learn more, researchers analysed data from a medical register of all live singleton, term births between 1992 and 2010 in Sweden, which included more than 1.7 million babies.
The register had information on women's height and weight early in pregnancy, as well as babies' medical problems and so-called Apgar scores.
The Apgar score assesses vitality using measures of heart rate, breathing, muscle tone, skin colour and activity on a scale from zero to 10. There can be many reasons for a low Apgar score, but the most common reason is lack of oxygen, lead author Dr. Martina Persson told Reuters Health in an email.
Persson worked on the study at the Karolinska Institutet in Stockholm.
Less than one in 1,000 babies had an Apgar score between zero and 3 at five minutes after birth, and even fewer had that low a score at 10 minutes after birth.
Compared to babies of normal-weight mothers, babies with overweight mothers were 32 per cent more likely to have an Apgar score that low at 10 minutes.
Babies of obese mothers were 57 per cent more likely to have a low Apgar score, and those of severely obese mothers were 80 per cent more likely.
A newborn's risk of seizures also increased with maternal weight. For instance, babies of severely obese mothers were twice as likely to have a seizure as those of mothers with a healthy weight.
The increased risks were similar for meconium aspiration, which happens when the baby releases stool in the womb and inhales the stool-tainted amniotic fluid.
"Meconium release is a sign of fetal stress," Persson said. "Meconium aspiration may give severe breathing problems in the newborn and is associated with birth asphyxia and low Apgar scores."
"Meconium aspiration and seizures could be serious in the immediate newborn period although still the majority of these children will be healthy," Blomberg told Reuters Health in an email.
Researchers don't know why these risks, which all relate to lack of oxygen, go up for babies of overweight and obese women, Persson said.
Obesity in pregnant women has been associated with metabolic changes and inflammation, which could affect the placenta and fetal environment in a way that leads to low oxygen levels and more fetal growth, she noted.
Also, larger babies, often born to larger mothers, may be more likely to experience trauma during delivery, which could result in lack of oxygen, she said.
"One must bear in mind that even though these conditions are potentially very dangerous for the baby, the absolute risks for the studied outcomes are low," Persson said.
Even with the most obese mothers, the risk of infants having a low Apgar score at five minutes was still only 0.24 per cent, or less than three babies out of every 1,000.
In addition to encouraging prospective mothers to strive for a healthy weight, doctors can closely monitor babies during labour and delivery, which likely reduces the risk of lack of oxygen at birth, she said.
"Enjoy your pregnancy!" Persson said. "Try to eat healthy and be physically active. Seek support from your midwife in order to change bad eating habits and try not to gain too much weight during pregnancy."