Adverse outcomes of assisted birth lowest at 39 weeks


In a recent study, rates of infant mortality were lowest among patients who delivered at 39 weeks of gestation.

Adverse outcomes of assisted birth lowest at 39 weeks | Image Credit: © WavebreakMediaMicro - © WavebreakMediaMicro -

Adverse outcomes of assisted birth lowest at 39 weeks | Image Credit: © WavebreakMediaMicro - © WavebreakMediaMicro -

According to a recent study published in JAMA Network Open, the lowest perinatal risk with infertility treatment is seen when delivery occurs at 39 weeks of gestation.

Infertility therapy was administered to 12.2% of female individuals from 2015 to 2019, according to the National Center for Health Statistics. In 2018, about 2% of births in the United States were performed using assisted reproductive technology (ART). 

Increased risks of perinatal mortality, stillbirth, and low birth weight are observed in conception through ART compared to spontaneous pregnancies, but it is unknown if these risks are because of ART use or underlying conditions leading to ART use. Currently, there is not a standard recommendation for when deliveries conceived with infertility treatment should occur.

To determine the gestational age when stillbirth risks are most balanced with neonatal comorbidities and mortality, investigators conducted a population-based retrospective cohort study. Data between January 1, 2014, and December 31, 2018, was collected from Linked Birth/Infant Death and Fetal Death Records.

The balance of the risks of delivery in each week of gestation from 37 to 42 weeks with the risks of delivery in the following week was measured as the primary outcome of the study. Risk of delivery was defined as, “the composite rate of infant death and neonatal morbidity incurred at a given week of gestation per 10,000 deliveries.”

One category of infertility treatment included fertility enhancing drug use, artificial insemination, or intrauterine insemination, while the other category was use of ART. Gestational age was determined by the best obstetrical estimate in a patient’s birth record, measured using the last menstrual period and other clinical parameters.

Exclusion criteria included birth at a gestational age under 37 weeks or of 43 weeks or more, having multiple gestations in pregnancy, preeclampsia or eclampsia, gestational or chronic hypertension, preexisting or gestational diabetes, and unknown diabetes or chronic hypertension history.

Stillbirth rate was measured as number of stillbirths per 10,000 ongoing pregnancies. Infant death rate was measured as number of infants born at a certain gestational age who died within 12 months per 10,000 live births of that gestational age. Neonatal morbidity was considered seizures, ventilation of at least 6 hours, neonatal intensive care unit admission, and an Apgar score of 3 or lower at 5 minutes.

There were 340,728 pregnancies where infertility was used, with a mean gestational age of 39.2 weeks. Of these, 178,448 were included in the analysis. Stillbirth was seen in 0.14% of included pregnancies and infant death in 0.07%. Infertility was seen more often in pregnancies with non-Hispanic White, nulliparous, and patients aged 35 years or older.

Preterm delivery was seen more often in pregnancies with infertility treatment than spontaneous pregnancies. A higher small for gestational age rate was seen in the stillbirth and infant death groups compared to the livebirth group.

For pregnancies with infertility treatment, stillbirth rates increased with each progressive week of gestational age, with the lowest being 3.1 per 10,000 births at 37 weeks and the highest being 21 per 10,000 births at 42 weeks. Similar trends were seen for pregnancies with ART, at 2.5 per 10,000 births at 37 weeks and 23.6 per 10,000 births at 42 weeks.

Infant death was lowest at 39 weeks, at 6.2 per 10,000 births for infertility treatment and 5.2 per 10,000 births for ART. Overall mortality and morbidity risk increased with each subsequent week of gestation, with the relative risk of delivery in the subsequent week at week 39 being greater than the risk of delivery.

These results indicated the lowest perinatal risk at week 39 when compared to the subsequent week of gestation. Investigators concluded early-term and late-term delivery increase the risks of adverse outcomes among patients conceiving with infertility treatment.


Hamilton I, Martin N, Liu J, DeFranco E, Rossi R. Gestational age and birth outcomes in term singleton pregnancies conceived with infertility treatment. JAMA Netw Open. 2023;6(8):e2328335. doi:10.1001/jamanetworkopen.2023.28335

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