Multiple pregnancies in HK: Prevalence up, perinatal mortality rate down in 2000–2019

Total perinatal mortality rate in multiple pregnancies showed a 45.4 percent decrease between 2000–2009 and 2010–2019 despite an increased prevalence of multiple pregnancies in Hong Kong during the same period, researchers from the Chinese University of Hong Kong (CUHK) have reported.

According to the researchers, the reduction in total perinatal mortality rate is related to reductions in stillbirth and late neonatal death in multiple pregnancies as a result of improved antenatal care and neonatal intensive care. [Hong Kong Med J 2022;doi:10.12809/hkmj2210153]

“Designated regular ultrasonography and antenatal clinical examinations, beginning in the first trimester, are essential for reducing perinatal mortality in multiple pregnancies, particularly when a monochorionic placenta is present,” they wrote. “Territory-wide monitoring of perinatal mortality is needed to maintain the standard of perinatal care in Hong Kong.”

In the retrospective study, the researchers investigated the prevalence and causes of perinatal mortality among multiple pregnancies in Hong Kong between 2000 and 2019. Analysis was based on records of all multiple pregnancies delivered at the Prince of Wales Hospital, which serves a population of approximately 1.7 million in New Territories East with an obstetric unit that receives referrals of complicated multiple pregnancies from other hospitals.

During the 20-year study period, there were 2,126 multiple pregnancies, 97.7 percent (n=2,077) of which were twin pregnancies. Triplet and quadruplet pregnancies accounted for 2.26 percent (n=48) and 0.05 percent (n=1) of the multiple pregnancies, respectively.

The prevalence of multiple pregnancies increased from 1.41 percent in 2000–2009 to 1.91 percent in 2010–2019 (p<0.001), due to increases in both monochorionic (from 0.52 percent to 0.60 percent) and non-monochorionic (from 0.87 percent to 1.31 percent) multiple pregnancies.

Total perinatal mortality rate of multiple pregnancies decreased from 25.32 per 1,000 births in 2000–2009 to 13.82 per 1,000 births in 2010–2019 (p=0.006).

“The rate of stillbirth decreased from 14.72 to 7.68 per 1,000 births [p=0.026] because of close antenatal ultrasonographic monitoring, as well as foetal intervention including foetoscopic laser coagulation,” the researchers noted. “The rate of late neonatal death decreased from 4.78 to 1.16 per 1,000 births [p=0.030] because of a reduction in rate of preterm deliveries before 34 weeks of gestation [from 18.5 percent to 15.2 percent; p=0.006], as well as improvements in neonatal intensive care that led to reduced mortality rate among babies delivered at 31–33 weeks of gestation [from 19.23 to 0 per 1,000 live births; p=0.035].”

While the rate of neonatal death was significantly higher in triplet vs twin pregnancies (42.25 vs 6.81 per 1,000 births; p=0.001), stillbirth rates did not differ significantly between the two groups (13.89 vs 10.35 per 1,000 births; p=0.663).

Multiple pregnancies with a monochorionic component showed higher rates of stillbirth (18.61 vs 6.36 per 1,000 births; p<0.001), late neonatal death (5.62 vs 1.07 per 1,000 births; p=0.009), perinatal mortality (26.88 vs 10.25 per 1,000 births; p<0.001) and total mortality (32.39 vs 11.31 per 1,000 births; p<0.001) vs those without a monochorionic component.

Compared with perinatal mortality in singleton pregnancies during the same 20-year period, which the researchers reported earlier, perinatal mortality rates in twin and triplet pregnancies were 3.6-fold and 10-fold higher, respectively (4.16 vs 14.93 vs 41.67 per 1,000 births; p<0.05). The 45.4 percent reduction in total perinatal mortality rate in multiple pregnancies between 2000–2009 and 2010–2019 was considerably larger than the 15.2 percent reduction reported for singleton pregnancies during the same period (from 4.54 per 1,000 births in 2000–2009 to 3.85 per 1,000 births in 2010–2019). [Hong Kong Med J 2022;28:285-293]