However, deeper plugs may be missed by this method. Use of a small forceps to gently part the vulvar lips to identify the plug in the vagina. Pregnancy Determination Pregnant mice will fail to return to estrus and will not breed when placed with male mice. Abdominal distention is apparent in most mice by 12-14 days of gestation. Mice with large litters may show distention slightly earlier.
Palpation takes practice, patience and a soft touch.
Gestation Gestation in mice varies slightly by strain and ranges from 19-21 days. Smaller litters are often carried longer than larger litters. If a mating takes place, the embryos resulting from the postpartum mating undergo developmental arrest and delayed implantation. Consequently, the delivery date of the pups from the postpartum mating may be delayed 4-5 days. Handling Pregnant Females Near term females with greatly distended abdomens should be disturbed as little as possible.