Recurrence risks for trisomies 13, 18, and 21.

Area of Science:

• Reproductive genetics
• Maternal-fetal medicine
• Birth defects epidemiology

Background:

• Previous trisomic pregnancies (13, 18, 21) may alter recurrence risk.
• Understanding recurrence risk is crucial for genetic counseling and reproductive planning.

Purpose of the Study:

• To determine if a prior pregnancy with trisomy 13, 18, or 21 increases the risk of these trisomies in subsequent pregnancies.
• To investigate the influence of maternal age at the time of the previous trisomic pregnancy on recurrence risk.

Main Methods:

• Utilized data from three Australian population-based birth defect registers.
• Analyzed 5,906 women with a previous trisomy pregnancy and their 3,713 subsequent pregnancies.
• Calculated relative risk (RR) of subsequent trisomies by comparing observed to expected rates based on maternal age.

Main Results:

• Increased risk for the same trisomy (13 or 18) after a previous affected pregnancy (RR=3.8), with higher risk for women under 35 (RR=7.8).
• Increased risk for trisomy 21 after a previous trisomy 21 pregnancy (RR=2.2), also higher for women under 35 (RR=3.5).
• A potential increased risk for a different trisomy following trisomy 21 was suggested (RR=1.4).

Conclusions:

• Women with a history of trisomic pregnancy have an elevated risk of subsequent trisomic pregnancies.
• This increased risk is particularly pronounced for women under 35 years old at the time of the previous affected pregnancy.
• Findings support enhanced surveillance and genetic counseling for women with a history of trisomy.