title: The placenta and zygosity of twins.
mesh_terms: D005321:Extraembryonic Membranes / Q000033:anatomy & histology; D005260:Female; D005306:Fertilization; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D009549:Nigeria; D010063:Ovum; D010920:Placenta / Q000033:anatomy & histology*; D011247:Pregnancy; D012744:Sex Ratio; D014427:Twins