| Locked twins | |
|---|---|
| Specialty | Obstetrics |
Locked twins is a rare complication ofmultiple pregnancy where two fetuses become interlocked duringpresentation before birth. It occurs in roughly 1 in 1,000 twin deliveries and 1 in 90,000 deliveries overall.[1] Most often, locked twins are delivered viaCaesarean section, given that the condition has been diagnosed early enough. The fetal mortality rate is high for the twin that presents first, with over 50% beingstillborn.
There are two types of locked twins: breech/vertex and vertex/vertex. In breech/vertex presentations, which are much more common, the first twin is in thebreech position, presenting feet-first, and the second is in thecephalic (vertex) position, presenting in the normal head-first manner.[2] In these cases, the chin of the first twin locks behind the chin of the second twin while in theuterus orbirth canal, preventingvaginal delivery.[3] In vertex/vertex presentations, where both twins are positioned for head-first delivery, the two heads become locked at thepelvic brim, preventing either fetus from passing through thepelvic inlet in a vaginal delivery.[2]
Contributing factors to the interlocking of twins include uterinehypertonicity, small fetal size, and reduced levels ofamniotic fluid followingrupture of the membranes.[3] It is more likely to occur in women with large pelvises, youngprimigravidae (young women in their first pregnancy), and pregnancies withmonoamniotic twins.[1]
If locked twins are diagnosed in early delivery, before either twin is born, both fetuses can be delivered byCaesarean section. If one fetus has been partially born, attempts can be made to disimpact the twins manually, such as by theZavanelli maneuver, with a view to performing an assisted delivery withventouse orforceps.[4] If the diagnosis is made only after the first locked twin has died in the birth canal, or if it is not expected to survive, the first twin may bedecapitated and its head pushed up to allow safe delivery of the second twin.[2][4]
At least one case has been reported wherehexoprenaline was used to relax the uterinesmooth muscle to thereby temporarily inhibit labour and disimpact the fetal heads.[1]
Since locked twins are often diagnosed in the late stages of delivery, it is often too late to intervene to save the life of the first twin and thus there is a high rate ofstillbirth, estimated to be over 50%.[1][5]
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