Cell-free DNA for single-gene conditions: what it can diagnose, and what it only screens

The edition in brief

Today's obstetrics and gynaecology edition centres on cell-free fetal DNA. A Scientific Impact Paper in BJOG (11 October) sets out how fetal DNA in maternal blood can test for single-gene conditions from about 8 weeks, and draws the line between diagnosis, where a known familial variant is targeted, and screening. A prospective US study of 2,212 carriers shows why that line matters: cfDNA fetal risk screening for cystic fibrosis, spinal muscular atrophy and haemoglobinopathies had sensitivity 94.4% and specificity 99.5%, but a positive predictive value of only 58.6%, so a high-risk result needs diagnostic confirmation. A Cochrane review of 35 trials found post-discharge home visits for preterm and low-birthweight infants likely raise breastfeeding at six months (RR 1.26), and that more intensive visits with community-initiated kangaroo mother care, tested largely in India, likely reduce six-month mortality (HR 0.75). A randomised trial of 350 people considering tubal sterilisation found a patient-facing website improved contraceptive knowledge (61% vs 52% correct at 3 months) and raised interest in implants without lowering sterilisation preference. A secondary analysis of 800 births found perineal massage with warm compresses did not increase postpartum perineal pain; anal sphincter injury and episiotomy drove pain. The pearl is the rectal examination before every perineal repair.