On day 42 of pregnancy, if progesterone is below 15nmol/L, while ultrasound suggests fetal dysplasia, birth control is not recommended at this time. Progesterone is the progesterone that maintains pregnancy and its most important role in early pregnancy is to promote endometrial proliferation, facilitate embryo implantation and inhibit uterine contractions. Low progesterone may be due to insufficient luteal function to produce less progesterone or due to abnormalities in the fetal development itself. Usually, a pregnant woman who is 42 days pregnant and has progesterone below 15 nmol/L indicates a possible risk of miscarriage or ectopic pregnancy. If the progesterone is consistently below 15 nmol/L and the doubling of the HCG test is poor, along with an ultrasound suggesting fetal dysplasia, then fertility preservation is not recommended. If it is simple low progesterone, pregnant women can take oral fetal preservation drugs and intramuscular progesterone for fetal preservation treatment. If the fetus itself is poorly developed, it is possible that the fetus will stop growing when it reaches a certain level even if the fetus is forced to keep the fetus.