Monoamniotic twins

[1] Other obscure possibilities include multiples sets where monoamniotic twins are part of a larger gestation such as triplets, quadruplets, or more.

[4] Further ultrasounds with high resolution doppler imaging and non-stress tests help to assess the situation and identify potential cord problems.

[1] Cord entanglement and compression generally progress slowly, allowing parents and medical caregivers to make decisions carefully.

[1][4] Regular and aggressive fetal monitoring is recommended for cases of monoamniotic twins to look for cord entanglement beginning after viability.

[10][8] A retrospective study in 2016 argued that there is evidence vaginal delivery can be equally safe and reduce complications for some monoamniotic twins[11] but this finding has not been incorporated into clinical guidelines.

Various types of chorionicity and amniosity (how the baby's sac looks) in monozygotic (one egg/identical) twins as a result of when the blastocyst or embryo splits
Abdominal ultrasonography of monoamniotic twins at a gestational age of 15 weeks. There is no sign of any membrane between the fetuses. A coronal plane is shown of the twin at left, and a sagittal plane of parts of the upper thorax and head is shown of the twin at right.