Expansion
Combined test, quadruple test, anomaly scan and infectious disease screening
Expansion
First trimester
- Dating scan at 10 to 14 weeks
- Combined test at 11 to 14 weeks: nuchal translucency, beta hCG and PAPP-A, with maternal age, screening for trisomy 21, 18 and 13
- Booking bloods: full blood count, blood group and antibodies, haemoglobinopathy screening, and infectious disease screening for HIV, hepatitis B and syphilis
- Urine culture for asymptomatic bacteriuria, which is treated in pregnancy
Second trimester
- Quadruple test at 14 to 20 weeks, for women who present too late for the combined test: AFP, hCG, unconjugated oestriol and inhibin A. It screens for trisomy 21 only
- Anomaly scan at 18 to 21 weeks, examining 11 conditions including anencephaly, spina bifida, cardiac defects, diaphragmatic hernia, gastroschisis, exomphalos and skeletal dysplasia
Patterns worth knowing
| AFP | hCG | Oestriol | Inhibin A | |
|---|---|---|---|---|
| Trisomy 21 | Low | High | Low | High |
| Trisomy 18 | Low | Low | Low | Low |
| Neural tube defect | High |
Non-invasive prenatal testing (NIPT) analyses cell free fetal DNA in maternal plasma from 10 weeks. It has very high sensitivity for trisomy 21, but it remains a screening test with false positives from confined placental mosaicism and vanishing twin, so a positive result must be confirmed.
Diagnostic tests: chorionic villus sampling from 11 weeks and amniocentesis from 15 weeks, each carrying a miscarriage risk of roughly 0.5 per cent or less in experienced hands.