Cesarean Birth Effects: Baby Weight Drops, Pregnancy Gets Shorter

Newborn babies are getting lighter and more women have been giving birth earlier in the U.S. These are the major changes in the country that researchers found linked to the increasing number of cesarean deliveries and inductions.



A new study, published in the journal Demography, found that birth weights have dropped significantly across the country in the past decades. The average pregnancy period also decreased by nearly a week.

Earlier research showed that birth weights declined by 67 grams since 1990 while the average length of pregnancy decreased from 40 weeks to 39 weeks in the U.S. However, at the time health experts did not determine what caused the trend.

In the latest study, researchers found that cesarean deliveries also increased in the same period. Between 1990 and 2013, the number of reported procedures climbed from 25 percent to 31.2 percent.

To determine the link between cesarean effects and changes in birth weight and pregnancy period, researchers analyzed records from the National Vital Statistics System. The team looked into more than 23 million single births to healthy mothers from 1990 to 2013.

They then used the data to create a simulation of what would have happened if cesarean and induction rates did not increase in that period.

“We found that the decline in birth weight would not have happened if it were not for the rapid increase in these obstetric interventions,” Andrea Tilstra, lead study author and a PhD candidate at the University of Colorado Boulder, said in a statement. “In fact, birth weights would have gone up.”

Results showed that with lower cesarean deliveries the average birth weight would have increased by 12 grams. Nearly 18 percent of births in 2013 would have also happened later, researchers said.

The team noted that the fetus can gain significant weight in the final weeks of pregnancy. Tilstra noted that changes in birth time and weight can have public health consequences, such as poor long-term health and lower educational attainment of children.

However, the researchers noted inductions and cesarean deliveries remain medically necessary. But doctors should reconsider conducting the procedures in healthy women.

“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,” Tilstra added. “If something is not obviously medically necessary it is important to ask why it's happening.”

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