Background Cystic hygroma (CH), is a congenital lymphatic malformation frequently detected in antenatal ultrasound scanning commonly associated with chromosomal defects. It also occurs as an isolated finding or in conjunction with other congenital anomalies. It is not understood whether CH is more common in foetuses affected by another (otherwise isolated) congenital anomaly than in foetuses not so affected; we investigate this link here.

Methods Cases analysed here were born between 01/01/2005 and 31/12/2012, identified with CH at any gestation during pregnancy and reported to the East Midlands and South Yorkshire Congenital Anomaly Register. The rate of CH prevalence in the population affected by another “isolated” anomaly was compared to the rate in the birth population.

Results 45% of CH cases were associated with a chromosomal anomaly, 7% were affected by a syndrome or by multiple other congenital anomalies and 38% occurred in isolation; 10% were affected by another “isolated” congenital anomaly. The regional birth prevalence rate for CH is 10.4 per 10,000 births (CI 9.6, 11.2) compared to 59.8 per 10,000 births (CI 46.4, 75.9) affected by an “isolated” anomaly, giving a risk ratio of 5.77 (CI 4.48, 7.41).

Conclusion A case with an otherwise isolated congenital anomaly is almost six times as likely to be affected by CH. However, this translates to only a small increase in absolute risk (an extra 50 cases per 10,000 births). However, care should be taken in CH cases to identify or exclude the presence of additional isolated anomalies, as well as chromosomal defects.