Predicting preterm delivery by measuring cervical length
Dr Kelly Hughes
Spontaneous preterm birth, defined as a baby being born before 37 completed weeks of pregnancy, is the leading cause of perinatal and early childhood mortality worldwide. While a short cervix (<25mm) measured with vaginal (internal) ultrasound is an important warning sign, a new study led and authored by Dr Kelly Hughes, Department of Obstetrics and Gynaecology, School of Clinical Sciences, has provided a more in-depth analysis of data than has previously been available, and been able to demonstrate the relationship between cervical length and risk of preterm birth with more precision, offering a clearer roadmap for pregnancy care.
The study titled “Prognostic value of cervical length for spontaneous preterm birth in asymptomatic women with singleton pregnancy: An individual participant data meta-analysis”, gathered the raw data of over 90,000 women from 27 different studies across 12 countries to examine patterns that smaller, individual studies might have missed. The most significant discovery was that the relationship between cervical length and preterm birth follows an L-shaped curve.
For women with a cervical length of 40mm or more, the odds of preterm birth are very low and stays stable but as soon as the measurement drops below 40mm, the risk begins to rise steeply. Compared to a woman with a 40mm cervix, a woman with a 30mm measurement has twice the odds of a spontaneous preterm birth. If the measurement is 20mm, that risk jumps, with the odds more than six times higher.
There were also other factors that were considered and they included whether the women had previous surgeries, past preterm births and even uterine shapes. A previous preterm birth, for example, appears to be a more important predictor of preterm birth in the next pregnancy than the cervical length.
Dr Hughes said “The study confirms that measuring the cervix with vaginal ultrasound at the 20-week scan is a highly effective way to predict risk and that understanding these specific risks, doctors can better target treatments to the women who need them most”.
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