3.7 Inclusion of Pregnancy Outcomes
Surveillance programmes aim to ascertain congenital anomalies among all pregnancy outcomes – live births, fetal deaths and terminations of pregnancy – if possible (see Fig. 3.12). Some countries have the ability and resources to ascertain all or most of these outcomes when they occur relatively late in pregnancy, but it is extremely difficult to systematically ascertain those occurring prior to 28 weeks’ gestation and, in particular, those in which the pregnancy is terminated.
For these reasons, if prenatal ascertainment of congenital anomalies is not an available option in a given catchment area, it would be more feasible initially to limit the ascertainment to live births and to fetal deaths occurring at 28 weeks’ gestation or older, or, alternatively, with a birth weight of at least 1000 g (if gestational age is not available). However, in many countries and settings, ascertainment among live births alone is a significant limitation that can lead to unreliable rates and trends, particularly for conditions with a high rate of loss prior to 28 weeks’ gestation (e.g. anencephaly). If a country has the capacity to ascertain cases prior to 28 weeks’ gestation, doing so can help provide a more accurate estimate of the prevalence of a condition such as anencephaly.
Programmes interested in more detailed information on inclusion of prenatal diagnosis in congenital anomaly surveillance can find some useful and practical suggestions and tips in the guidelines developed by the National Birth Defects Prevention Network (NBDPN) in the USA (14).
Fig. 3.13 and Fig. 3.14 show how inclusion of the different types of pregnancy outcomes has improved case ascertainment for anencephaly and spina bifida in 14 countries. It is important to note that programmes that include terminations of pregnancy find the terminations based on monitoring prenatal diagnosis. For example, the majority of fetuses with anencephaly are ascertained through fetal deaths or terminations.
Fig. 3.13 indicates that in Wales, Tuscany (in Italy) and the Northern Netherlands, for example, 100% of fetuses with anencephaly are ascertained through pregnancy terminations, while in Utah (in the USA), 50% are ascertained through terminations, 40% through fetal deaths and only 10% as live births. Similarly, as Fig. 3.14 indicates, a much greater proportion of fetuses with spina bifida in Wales, Tuscany and Northern Netherlands are ascertained through pregnancy terminations, as compared to the other countries, regions or states represented.