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Source: Gilbert RE, Tookey PA. Perinatal mortality and morbidity among babies delivered in water: Surveillance study and postal survey. BMJ 1999;319:483-487.
Design/Setting/Subjects: Over a two-year period (1994-1996), all 1,500 consultant pediatricians in the British Isles were surveyed each month on whether they knew of any births that resulted in perinatal death or hospital admission within 48 hours following labor or delivery in water. Detailed information on cases was gathered. As checks on accuracy, regional coordinators were contacted to see whether they knew of additional unreported cases, and findings were compared to the confidential inquiry into stillbirths and neonatal death (a mandatory, regional notification system). Additionally, in 1995 and 1996 a mail questionnaire was sent to all National Health Service units in England and Wales.
Results: Reported water births constituted 0.6% of all deliveries. Of 4,032 water births during the study period, there were five perinatal deaths. Two of these were stillborns. The three postpartum deaths were associated with abnormal findings; a baby who died eight hours after birth had hypoplastic lungs; one baby died at three days of age of neonatal herpes; and the third died of intracranial hemorrhage 30 min after a precipitous delivery.
There were 32 other admissions for special care, resulting in a risk of 8.4/1,000 live births, including 15 with lower respiratory tract problems (of which one was diagnosed with freshwater drowning). Two babies had evidence of streptococcal pneumonia. Five cases of hypoxic ischemic encephalopathy or perinatal asphyxia were diagnosed; 15 had a variety of other diagnoses.
Compared with a large data set of low-risk women who delivered conventionally in the North West Thames region, there was no increased risk of perinatal mortality for babies delivered in water. Special care admission rates were significantly lower for babies delivered in water than those delivered conventionally.
Comments: As the researchers point out, the numbers of perinatal death or admission for special care were small and the confidence intervals wide. (Only a relative risk of 3.6 or greater would have been picked up by this study). Perinatal mortality estimates may be more accurate than estimates of special care admissions. Researchers were confident that they missed no deaths (because no additional deaths were identified through the confidential inquiry into stillbirths and infant deaths), but note that the number of water births may well have been underestimated, so the actual denominator may well be larger. In other words, the figure for perinatal mortality is an upper estimate. However, there may well be underreporting of admissions for special care following water birth, so it is possible that this number is underestimated. Two admissions may have been due to water aspiration (although it is thought that babies don’t breathe until exposed to air, animal experiments have shown that this inhibitory mechanism can be overridden by sustained hypoxia). Although this study clearly shows no substantially increased risk of perinatal mortality or morbidity among babies born in water, compared to those born conventionally, small increases in risk cannot be ruled out.