Older maternal age, higher BMI tied to increased NTSV Caesarean delivery rate

Elaine Soliven
22 Feb 2021

Older maternal age and higher body mass index (BMI) were associated with an increased risk of nulliparous, term, singleton, vertex (NTSV) Caesarean delivery, according to a study presented at SMFM 2021.

Using US natality records from 2016–2018, the researchers analysed 3,671,007 deliveries, of which 25.9 percent were an NTSV Caesarean birth. Obstetric, demographic, and medical risk factors, such as maternal age, BMI, and pre-gestational diabetes, were assessed. The primary outcome of the study was the rate of Caesarean delivery. [SMFM 2021, abstract 188]


There was a higher risk of NTSV Caesarean delivery among women who were aged 35–39 (risk ratios [RRs], 1.55 [unadjusted] and 1.51 [adjusted]) and 40–54 years (RRs, 2.11 [unadjusted] and 1.99 [adjusted]) compared with women aged 19–34 years.

Similarly, the risk of NTSV Caesarean delivery was higher among women with BMIs of 25.0–29.9, 30.0–34.9, and 35.0–39.9 kg/m2 (RRs, 1.36, 1.65, and 1.96, respectively [unadjusted] and 1.32, 1.56, and 1.80, respectively [adjusted]) compared with those with a BMI of <25 kg/m2.

An increased risk of NTSV Caesarean delivery was also noted in women with a history of pre-gestational diabetes (RRs, 2.13 [unadjusted] and 1.55 [adjusted]).

When the Caesarean deliveries without trial of labour (n=585,594) were excluded, maternal ages of 35–39 (adjusted RR, 1.96) and 40–54 years (adjusted RR, 3.12) were still associated with an increased risk of Caesarean delivery compared with maternal age of 19–34 years.

“[Of note,] these associations retained significance in adjusted analysis,” said study author Dr Maria Andrikopoulou from Columbia University Irving Medical Center in New York, New York, US.

Overall, an increased NTSV Caesarean delivery rate was observed among women who had ≥1 of these risk factors, particularly maternal age of ≥35 years, BMI of ≥30 kg/m2, or pre-gestational diabetes, than women without any of these risk factors (37.2 percent vs 20.7 percent).

“In conclusion, higher BMI and older maternal age were associated with 50–100 percent increased risk of NTSV Caesarean [delivery],” said Andrikopoulou.

“The distribution of these risk factors may be important in interpreting hospital-level Caesarean rates and in questioning the validity of the unadjusted NTSV rate as a quality indicator,” she added.
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