A fetus that assumes a "head down" position during labor is said to have a cephalic presentation. The infant may still be oriented in a number of directions, such as vertex position, with the occiput anterior and the face and front of the body toward the mother's spine, face presentation with the head tilted back into full neck extension, or occpito-posterior, in which the occiput is against the sacrum. In a transverse presentation, the fetus is sidelong, while a breech presentation the fetus' head is superior while the legs are inferior.

The designations for parity are as follows:

• Nulliparous: Never delivered a child or carried a pregnancy past 20 weeks
• Primiparous: Has given birth once or is about to give birth for the first time
• Multiparous: Has given birth twice
• Grand multiparous: Has given birth three or more times

Contractions in labor are stimulated by oxytocin, a nonapeptide hormone produced in the hypothalamus and stored in the posterior pituitary. Oxytocin also triggers postpartum contractions in order to compress the lax uterine wall and reduce postpartum bleeding. Prolactin is a hormone essential to breast-milk production, while estrogen and progesterone have a multitude of roles in both fetal and placental development.  

Oxytocin, a nonapeptide hormone produced in the hypothalamus, has a variety of physiological roles. It increases trust, generosity, and other markers of social cohesion. In intimate relationships, it increases feelings of affection, love, sexual arousal, and contentment. It is an important hormone in labor, as it triggers contractions both during labor and postpartum in order to reduce bleeding and uterine size after delivery. It also acts as an immune modulator in wound healing. It does not, however, increase appetite - studies have shown it to have the opposite effect, acting as an appetite suppressant in human and animal models. 

During the later stages of labor, the cervix, normally a four centimeter-long muscular sphincter, releases its mucus plug, then thins and shortens. The release of the mucus plug is termed the "bloody-show," and the thinning and shortening of the cervix is called effacement. Cervical effacement is almost always accompanied by cervical dilation, or a widening of the os in order to allow passage of the fetus. This all happens in the transition phase of labor. 

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.