<Tr> <Th> DiseasesDB </Th> <Td> 1631 </Td> </Tr> <Tr> <Td_colspan="2"> (edit on Wikidata) </Td> </Tr> <P> A cephalic presentation or head presentation or head - first presentation is a situation at childbirth where the fetus is in a longitudinal lie and the head enters the pelvis first; the most common form of cephalic presentation is the vertex presentation where the occiput is the leading part (the part that first enters the birth canal). All other presentations are abnormal (malpresentations) which are either more difficult to deliver or not deliverable by natural means . </P> <P> The movement of the fetus to cephalic presentation is called head engagement . It occurs in the third trimester . In head engagement, the fetal head descends into the pelvic cavity so that only a small part (or none) of it can be felt abdominally . The perineum and cervix are further flattened and the head may be felt vaginally . Head engagement is known colloquially as the baby drop, and in natural medicine as the lightening because of the release of pressure on the upper abdomen and renewed ease in breathing . However, it severely reduces bladder capacity, increases pressure on the pelvic floor and the rectum, and the mother may experience the perpetual sensation that the fetus will "fall out" at any moment . </P>

What is the meaning of vertex presentation in pregnancy
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