The present place of routine ultrasound screening.

The value of routine ultrasound examinations is illustrated in Table 3. Ultrasound examination may of course be indicated in early pregnancy on clinical grounds. If it is not, we recommend that all patients should have measurement of the BPD between 16 to 18 weeks' gestation even if they have optimal menstrual histories. It is preferable to have a routine ultrasound service if a MSAFP programme is offered because, although it is possible to scan only patients with a raised MSAFP, prior knowledge of gestational age helps in the timing of the sample and prevents concern in patients with inaccurate dates. At 16 to 18 weeks' gestation multiple pregnancies can be diagnosed reliably and many structural abnormalities can be detected even when the routine examination is performed by non-medically trained personnel. A fundal placenta at 16 to 18 weeks' gestation excludes the possibility of placenta praevia. Seeing the fetus on the ultrasound screen and watching fetal movements strengthens parental feelings towards pregnancy. A repeat ultrasound examination in the third trimester to measure AC is superior to clinical means of detecting growth retardation. Placental localization at this gestation is accurate and has removed the need for the hazardous 'examination under anaesthetic'. If facilities are available we recommend that every patient has a repeat scan in the third trimester. If facilities are insufficient then we recommend that high risk patients have serial scans and that other patients have SFH measurement at each antenatal visit, and that only those that have a low SFH should have repeat ultrasound examinations. Until the day arrives when there is sufficiently trained personnel, adequate equipment and time to perform detailed examinations of all fetuses at 16 to 18 weeks' gestation, together with serial examination and measurement of all growth parameters, we feel the above schema makes the best use of available facilities.