defects in implantation and gastrulation

what leads to placenta previa

implantation close to internal os of cervix

common places in ectopic pregnancy

abdominal cavity, ovary or uterine tube

molar pregnancy

trophoblast develops a placental membrane with little to no embryonic tissue but secretes hCG

caudal dysgenesis/ sirenomelia

insufficient mesoderm formation in the caudal region

sacrococcygeal teratomas

caused by remnants of primitive streak in that region

sonic hedgehog

gene for establishing midline

holoprosencephaly

issue with the cells in the anterior midline of the germ disc

situs solitus

normal positioning of internal organs

situs inversus

mirrored arrangement of internal organs

situs ambiguous

different organ positioning with respect to symmetry where one or more organs are abnormally reversed in position

serotonin (5-HT)

involved with midline and laterality defects