Letter to the editor

Abstract

To the Editors: The November issue of the American Journal of Obstetrics and Gynecology included 3 papers on monochorionicity which rightfully deserved the Editorial by Dr Malone, who aptly pointed to the recognized relationship between cerebral palsy and multiple births.1.Malone F.D. Monochorionic pregnancy–where have we been? Where are we going?.Am J Obstet Gynecol. 2003; 189: 1308-1309Abstract Full Text Full Text PDF PubMed Scopus (14) Google Scholar However, the significance of the association between monochorionicity and cerebral palsy should be critically and quantitatively reviewed. First, fewer monozygotic (and monochorionic) twins are found among iatrogenic compared with spontaneous conceptions (∼10% to 15% vs ∼33%, respectively). Second, there are probably more dichorionic than monochorionic pairs among iatrogenic monozygotic twins. This supposition explains the differences in estimated monzygosity rates following single embryo transfers compared with sonographically diagnosed zygotic splitting.2.Blickstein I. Jones C. Keith L.G. Zygotic-splitting rates after single-embryo transfers in in vitro fertilization.N Engl J Med. 2003; 348: 2366-2367Crossref PubMed Scopus (80) Google Scholar Third, twin-twin transfusion affects only 10% to 15% of monochorionic twins, and only a part of these cases are severe enough to cause fetal demise or merit sophisticated therapy. Fourth, the increased risk of cerebral palsy in monochorionic twins, irrespective of twin-twin transfusion, is primarily associated with single fetal death,3.Blickstein I. Cerebral palsy in multifoetal pregnancies.Dev Med Child Neurol. 2002; 44: 352-355Crossref PubMed Google Scholar, 4.Pharoah P.O. Adi Y. Consequences of in-utero death in a twin pregnancy.Lancet. 2000; 355: 1597-1602Abstract Full Text Full Text PDF PubMed Scopus (186) Google Scholar a combination occurring in about 1% of all twin gestations. Finally, population-based studies relating cerebral palsy to zygosity should be interpreted with care because they often use epidemiologic estimations rather than zygosity/chorionicity assessments.3.Blickstein I. Cerebral palsy in multifoetal pregnancies.Dev Med Child Neurol. 2002; 44: 352-355Crossref PubMed Google Scholar, 4.Pharoah P.O. Adi Y. Consequences of in-utero death in a twin pregnancy.Lancet. 2000; 355: 1597-1602Abstract Full Text Full Text PDF PubMed Scopus (186) Google Scholar It follows that complicated monochorionicity has an insignificant contribution to the cerebral palsy rates among twins, especially in centers with busy infertility clinics, where iatrogenic conceptions account for about half of the multiple births.3.Blickstein I. Cerebral palsy in multifoetal pregnancies.Dev Med Child Neurol. 2002; 44: 352-355Crossref PubMed Google Scholar In contrast, preterm birth low birth weight, and growth aberrations are by far more common and definitely more important in the pathogenesis of cerebral palsy in multiples.3.Blickstein I. Cerebral palsy in multifoetal pregnancies.Dev Med Child Neurol. 2002; 44: 352-355Crossref PubMed Google Scholar Obviously, every effort should be made to diminish neurologic damage in complicated twin-twin transfusion or in the extremely rare case of an acardiac twin. However, saving these twins cannot substantially alleviate the gloomy frequencies cited by Dr Malone.1.Malone F.D. Monochorionic pregnancy–where have we been? Where are we going?.Am J Obstet Gynecol. 2003; 189: 1308-1309Abstract Full Text Full Text PDF PubMed Scopus (14) Google Scholar From the point of public health, potential reduction of cerebral palsy by sophisticated interventions in complicated monochorionicity is much smaller compared with the estimated 8% contribution of assisted reproduction to the annual cerebral palsy rate in the US. Therefore, the only effective remedy is reducing the number of iatrogenic conceptions—the major contributors to the epidemic dimensions of multiples. Although I enthusiastically join the plea of Dr Malone for a large prospective study on the aftermath of monochorionicity, I think that a timely title for an Editorial should read: “Multiple pregnancy: Where have we been? Where are we going?”