Perinatal Outcomes in Twins: The Effect of Placental Abruption
Abstract & Commentary
Synopsis: Birth weight discordancy of > 15% for same sex and > 30% for different sex confer greatest risk of adverse perinatal outcomes in the absence of abruption. In the presence of placental abruption, these risks are further compounded. The results underscore the need for careful monitoring of twin pregnancies.
Source: Ananth CV, et al. Am J Obstet Gynecol. 2003; 188:954-960.
In obstetrical texts much has been made of the poor pregnancy outcomes associated with twin weight discrepancies of more than 20%. In a recent report, Ananth and colleagues have thrown another factor into the mix, placental abruption.
They looked at data from a "matched multiple birth file" for the United States from 1995 to 1997. The data involved 269,287 patients. Since information on zygosity was not available, they broke their results into same sex vs opposite sex twins.
The relative risk of abruption was 1.2 (CI, 1.1-1.4) for same sex twins with a 20% or greater discordance and 2.2 (CI, 1.7-2.8) for opposite sex twins with a 40% discordance. In nonabruptions, there was an increase in stillbirth, preterm births, and neonatal deaths when birth weight discordance exceeded 15% in same sex and 30% in different sex twins. Not surprisingly, abruption increased the risk for perinatal death even when discordance was a little as 5%.
Comment by John C. Hobbins, MD
Twins are emerging as one of the largest problems in obstetrics. Older figures indicated a prevalence of spontaneous twinning to be 1 in 80 pregnancies—one third of these being identical. Now, through ovulation stimulation and assisted reproductive techniques, the prevalence of twins is around 1 in 40 and much higher in those older than 35 years of age. The overwhelming majority of this increase is contributed by dizygous twinning.
This trend is alarming because, although couples desperately seeking fertility help are happy to have any kind of pregnancy, the chance of problems during and after pregnancy more than doubles. Also, we have shown from our own studies that the cost of maintaining twin pregnancies is 6 times that of a singleton, a fact that has substantial impact on the cost of health care.
There are 2 major reasons why twins require so much attention:
1. They tend to deliver earlier (10% of monozygotic twins and 5% of dizygotic twins deliver prior to 32 weeks); and
2. They have a higher rate of intrauterine growth restriction, with all its accompanying morbidity.
The good news is that, in the absence of anomalies (twins have a higher rate), intrauterine growth retardation (IUGR), and preterm birth, the majority of patients with twins sail through pregnancy without a hitch. The thrust of our attention should be directed toward identifying early which patients would be in the at-risk categories so that we can concentrate on them, while leaving the others alone so that they might enjoy a singleton-like pregnancy. Also, this could generate substantial cost savings.
The best time to assess this risk for preterm birth and IUGR is between 20 and 24 weeks. A cervical length examination by transvaginal ultrasound will give the clinician a better idea of risk for very early delivery (< 32 wks). For example, in a study by Souka and colleagues the risk of preterm birth at less than 32 wks with a cervix of < 2.5 was 47%.1 However, the risk of very early preterm birth with a cervix of > 4.0 is remarkably low with a negative predictive value exceeding 98%.
The twin IUGR story is just starting to unfold. Our yet unpublished data suggest that a 20% discordance is of much less importance if it does not involve IUGR of at least one twin. A 20% discordance in appropriate for gestational age (AGA) twin weight had little effect on time of delivery or days in the nursery. However, when the > 20% discordance involved a fetus that was below the 10th percentile, there was a significant decrease in age at delivery and a substantial increase in days spent in the nursery. Also, those with discordance in biometry at 20-24 weeks had far more morbidity than those in which the discordance occurred after 30 weeks, the latter having outcomes similar to concordant AGA twins.
Buried in the Ananth study data was an interesting fact: 63% of twins with a birth weight discordance of > 20% involved at least one twin with IUGR. This risk was much further elevated in the presence of placental abruption.
All of the above observations suggest there is a primary placental reason for IUGR and abruption that can be suspected early (20-24 wks) in pregnancy by biometry alone. Our recent research thrust has been in honing in on the placenta with new color Doppler techniques to identify the placentas that are struggling during a critical stage in branching angiogenesis.
Better yet, it is hoped that with a comprehensive examination in twins at 20-24 weeks, using biometry, transvaginal ultrasound, and sophisticated 2-D and 3-D Doppler methods, clinicians will be able to pick out the majority of patients whom we can leave alone.
1. Souka AP, et al. Obstet Gynecol. 1999;94:450-454.