title: [Determining factors in the intrauterine development of twins: possible effect of gestational age, sex and type of twins].
abstract: Authors present a study on 9,862 malformed newborns and 9,950 controls collected among 481,362 births monitored by Spanish Collaborative Study of Congenital Malformations (ECEML) from March 1976 to March 1985. Newborn twins (malformed and controls) had a significantly lower birthweight and mortality rate within first three days of life than singletons. Difference in birthweight was not dependent on gestational age. On the other hand, males and females of unlike-sexed twin pairs were heavier than males and females of like-sexed pairs, respectively. Malformation rates in twins and singletons were not significantly different; among twins, the higher figure corresponded to like-sexed pairs, and more specifically, to those in which both members of the pair were males. Possible influence of gestational age, sex and type of twinning (like or unlike sex) on the process of intrauterine development in twins, is discussed.
authors.affiliation: Cátedra de Anatomía II, Facultad de Medicina, Universidad Complutense, Madrid.
authors.forename: M A
authors.initials: MA
authors.lastname: Ramos-Arroyo
authors.forename: E
authors.initials: E
authors.lastname: Rodríguez-Pinilla
authors.forename: F
authors.initials: F
authors.lastname: Marcos Herrero
authors.forename: M L
authors.initials: ML
authors.lastname: Martínez Frías
mesh_terms: D001724:Birth Weight; D000013:Congenital Abnormalities / Q000453:epidemiology*; D005314:Embryonic and Fetal Development; D005865:Gestational Age; D006801:Humans; D007226:Infant Mortality; D007231:Infant, Newborn; D012737:Sex Factors; D013030:Spain; D014427:Twins
vernacular_title: Factores determinantes del desarrollo intrauterino en gemelos: posible efecto de la edad gestacional, sexo y tipo de gemelos.