The cervix is considered to be fully dilated at . This suggests the transition phase of active labor, in which the individual is instructed to bear down (push) in order to facilitate delivery. 

During a normal pregnancy, the volume of blood plasma increases by 50%. The erythrocyte count also increases, by as much as 30%. This may cause the hematocrit to appear lower than normal, due to dilution by the relatively larger increase in plasma. 

While research is still being conducted to determine the cause of nausea and vomiting of pregnancy, it generally correlates with the surge in human chorionic gonadotropin (hCH) that occurs in the first trimester. Estrogen may be another contributing hormone. Aldosterone, DHEA, and corticotropin-releasing hormone (CRH) have no apparent involvement.

Most pregnancy tests detect human chorionic gonadotropin (hCG), a hormone produced by the embryo that is detectable shorty after implantation (10-14 days after fertilization). The function of hormone is to mimic the effects of luteinizing hormone, ultimately preserving the corpus luteum, which secretes progesterone. The progesterone maintains and vascularizes the uterus, making it a more favorable environment for the implanted embryo.

The time frame correctly matched is at 20 weeks, the heartbeat is heard with a stethoscope although it may be heard with ultrasound as early as 10-12 weeks. Quickening usually occurs around 20 weeks as well. The eyes open later between 24-27 weeks, lanugo first appears between 13-16 weeks, and the sex is recognizable around 12 weeks. 

The neural tube forms from the neural plate during the fourth week of embryonic development, which is often before the mother knows of the pregnancy.

A teratogen is a substance that has been known to cause birth defects. Some teratogens include alcohol, tobacco, phenytoin, rubella virus, and tetracycline. Carcinogens are a subclass of mutagens which have been known to cause cancer-inducing mutations. Mutagens cause mutations in cellular DNA expression (which may or may not lead to cancer or any other pathological condition), and pyrogens are substance that cause fever.

The term for the development of specialized cell types is differentiation. This is a process by which pluripotent embryonic stem cells, all of which have the same genome, are methylated in various ways to "turn off" certain genes and leave other genes exposed for transcription. This allow cells to develop the specific features that they will require to perform their function as heart cells, neurons, etc. 

Over 85% of miscarriages occur in the first trimester. Less than 10% of miscarriages occur in the second trimester, and miscarriage in the third trimester is very rare and generally considered to be stillbirth or preterm delivery that result in loss of the baby due to complications (most often respiratory or digestive underdevelopment). 

While all of the hormones listed are important for development of a healthy embryo, the most important hormone for preventing early first trimester miscarriage is progesterone. This hormone is generally secreted by the corpus luteum in sufficient quantities to prevent the shedding of the endometrial lining after implantation. When progesterone is insufficient, the endometrium can be shed as in a regular menstrual period, resulting in loss of the pregnancy. In most cases this type of miscarriage can be easily prevented by supplementation with vaginal progesterone suppositories.