Twin birth: mode, timing and intrapartum management

The registrar's nightmare is not twin 1. Twin 1 behaves like a singleton and delivers like one. The nightmare is the ninety seconds after: the uterus suddenly half-empty, a baby swinging into a transverse lie, a CTG that was fine and now is not, and a decision about whether your hand goes inside or the woman goes to theatre. Everything below is preparation for those ninety seconds.^[1][11]

Overview and definition

Twins are classified two ways, and only one of them matters clinically. ^[3]

• Zygosity — monozygotic (one egg, splitting) or dizygotic (two eggs). Interesting for the family, largely irrelevant to management.
• Chorionicity and amnionicity — how many placentas and how many sacs. This is the operative variable: it drives surveillance, timing, and most of the excess risk. RANZCOG C-Obs 42 turns on it, and so does RCOG Green-top 51.^[3][4]

^{[3] [4] [5]}

References18ShowHide

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