Why have birth weights among babies in the US dropped? Study reveals

The study claims that the increasing rates of C-sections have also reduced the average pregnancy by nearly a week

Cesarean delivery or C-sections have been performed from the days of Julius Ceaser and before to save the lives of mothers and babies. The intervening procedure is often resorted to when normal birthing is marred by a complication. However, a new study suggests that rising rates of C-sections have led to a decline in the average weight of babies in the 23 years.

The study by researchers at the University of Colorado Boulder claims that not only has the birth weight of babies in the US declined due to the soaring rates of the procedure, but it has also reduced the average pregnancy by nearly a week.

"Our data indicate that there has been a dramatic shift in birth timing in this country, it is resulting in birthweight decline, and it is almost entirely due to changes in obstetric practices," said Ryan Masters, senior author of the study, in a statement.

23-year-old decline of average birth weight

Representational Picture Pixabay

Studies before the current one, have illustrated that after witnessing a rise for decades, birth weights noticed a decline in 1990, causing alarm among experts who were aware of the ill-effects of low birth weight. Hence, using data from the National Vital Statistics System, the researchers set out to ascertain the driving force behind the trend.

The authors examined over 23 million single babies born to healthy mothers between the years 1990 to 2013. Relying on demographic tools they plotted vital information such as birth weight, which week in the final trimester the birth occurred, and the manner in which the baby was birthed (ie) vaginal delivery, induced vaginal delivery, induction, and cesarean and cesarean delivery.

Following this, a simulation was run by the researchers to ascertain what the impact on birth weight would have been if cesarean and induction rates had not increased. Emphasising that birth weights would have seen an upward swing, Andrea Tilstra, lead author of the study, said, "We found that the decline in birth weight would not have happened if it were not for the rapid increase in these obstetric interventions."

Birth interventions on the rise

Representational Picture Pixabay

Firstly, the average duration of the pregnancy period decreased to 39 weeks from 40 weeks, and the concentration of overall births was between 37 and 39 weeks. Few stretched into 42 weeks. Secondly, the rate of cesarean deliveries rose from 25 percent in 1990 and 31.2 percent in 2013. Healthy women who were in weeks 37 to 39 of their gestation period were in the middle of this steep rise. From 12 percent in 1990 to 29 percent in 2013, induced labour more than doubled in 23 years.

Thirdly, the researchers found that had 18 percent of births in 2013 occurred in 1990 vaginally and without any induction, they would have occurred much later. As a fetus can gain a significant amount of weight towards the end of the pregnancy, this finding made an important difference, noted the researchers.

Most importantly, during the chosen study period, there was a decline of 67 grams in the average weight of the babies born. A rise of 12 grams would have been seen had the intervention rates remained stable. "By intervening in the pregnancy instead of allowing it to reach its natural finality we are shifting when birth happens, and that can have public health consequences," said Tilstra.

Some interventions necessary, but not always

Some inductions and deliveries through cesarean are an immediate life-saving medical demand in some cases the researchers point out. However, they also stress that the sharpest rise in birth interventions is among healthy women who have reached full-term but are shy of the due period.

Unlike many countries, physicians in the US have a larger autonomy in determining the need for a cesarean delivery note the author. Therefore, they suspect that the factor leading to the trend could be cultural and institutional considerations such as insurance levels or financial incentives at the hospital.

Representational Picture Wikimedia Commons

Tilstra clarified that she is not advising doctors to refrain from performing inductions or cesarean deliveries or asking mothers to refrain from undergoing the procedure. However, she expressed hope that the study will provide information that may aid parents and practitioners to weigh pros and cons.

"I hope it prompts physicians to take a step back and realize there can be broader public health impacts from these individual decisions, and I hope it reminds mothers that they have more autonomy in the birth process than they sometimes feel they do," she concluded.