NEW ORLEANS – The optimal time to deliver monoamniotic twins is right around 33 weeks, when the risks of intrauterine death and neonatal complications are both very low.
"Monoamniotic twin pregnancies are at extremely high risk of intrauterine death before 28 weeks’ gestation," Dr. Tim Van Mieghem said at the Pregnancy Meeting, sponsored by the Society for Maternal Fetal Medicine. "But with regular fetal monitoring and ultrasound, that risk is extremely low from 28 to 32 weeks."
Dr Tim van Mieghem
At the same time, the risk of neonatal complications decreases as the pregnancy advances. The fulcrum that balances both optimal outcomes is 33 weeks, 4 days.
To determine this, Dr. Van Mieghem looked at a retrospective cohort of monoamniotic twin pregnancies followed during 2003-2013 in Canada and Europe. The group comprised 193 pregnancies (386 fetuses); the investigators excluded conjoined twins and cases of twin reversed arterial perfusion. The rate of twin-twin transfusion syndrome was low (3%).
The rate of fetal anomalies was quite high (53; 14%), said Dr. Van Mieghem of the University Hospital of Leuven, Belgium. Twelve of the pregnancies were terminated. There were 28 double intrauterine deaths and 14 single intrauterine deaths. Most of these were caused by cord events; seven were iatrogenic.
Most of the fetuses (76%) were born alive at an average of 32 weeks’ gestation. Most of the mothers received corticosteroids (91%), and most deliveries were by cesarean section (97%). The mean birth weight was 1,749 g. The neonatal death rate was 5.7%.
The most common neonatal complications were respiratory; 80% of the infants needed respiratory support and 40% had respiratory distress syndrome. The rate of nonrespiratory complications was about 15%. Sepsis occurred in about 10%. The remainder of the complications were necrotizing enterocolitis, intraventricular hemorrhage, and periventricular leukomalacia.
The risk of intrauterine death decreased as the pregnancy advanced. At 24 weeks, it was about 5%, but by 28 weeks had dropped to a low of 1.4%. Thereafter, the risk began to rise, reaching about 7% by week 35.
The risk of neonatal complications also decreased as the pregnancy advanced. It reached its nadir of about 2% at around 28 weeks and stayed low until about 33 weeks, when it began to rise. By 34 weeks it was near 7%, but dropped to close to 0 shortly after 35 weeks.
"The risk curves intersected at 32 weeks, 4 days," Dr. Van Mieghem said. "Based on these curves, it seems prudent to deliver these fetuses at 32 weeks, when the risk of both intrauterine demise and neonatal complications is about 3%."
He added that there were no significant differences in neonatal outcomes between pregnancies that were monitored on an inpatient and outpatient basis. The gestational age at delivery was about a week earlier in inpatients (32 vs. 33 weeks.) The rate of fetal distress was slightly higher among inpatients (21% vs. 23%). The outpatient pregnancies resulted in larger infants (mean 1,827 g vs. 1,776 g).
The rate of nonrespiratory neonatal complications was about 9% in each group. However, significantly more infants in the inpatient group needed ventilation (76% vs. 63%). They were also on ventilation about a day longer (5 days vs. 4 days).
There were one single and two double intrauterine deaths in the outpatient group, and one single intrauterine death in the inpatient group. But because all of the outpatient deaths occurred before 28 weeks, Dr. Van Mieghem said they probably could not have been averted by inpatient management.
"If you were looking at the rate of truly preventable deaths, it likely would have been 0 in both groups," he said.
Dr. Van Mieghem had no financial disclosures.
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