Human Biology: Labor Physiology

Respiratory System

• During labor, oxygen consumption increases by about 100% in the second stage, similar to strenuous exercise.
• This increase in oxygen demand can lead to hyperventilation.
• Proper breathing techniques during labor can help prevent severe hyperventilation.

Temperature Regulation

• Increased muscular activity during labor can cause a slight temperature elevation (1°F).
• Diaphoresis, or sweating, helps cool the body through evaporation.

Fluid Balance

• Increased respiration and diaphoresis during labor lead to increased insensible water loss.
• Reduced oral intake, combined with increased fluid losses, can necessitate intravenous fluid replacement in prolonged labor.

Urinary System

• During labor, decreased fluid intake and increased water loss lead to concentrated urine with a high specific gravity (1.020-1.030).
• Trace amounts of protein in the urine are common due to increased muscle activity.
• Pressure from the descending fetal head on the bladder reduces bladder tone, making it harder to sense fullness.

Musculoskeletal System

• Relaxin, a hormone released by the ovaries, softens cartilage between bones, particularly in the symphysis pubis and the sacral/coccyx joints.

Gastrointestinal System

• Decreased blood flow to the digestive system and pressure from the contracting uterus reduce gastrointestinal activity during labor.
• Digestion and stomach emptying are slowed.
• Strong contractions may trigger loose bowel movements similar to menstrual cramps.

The Urinary System (Postpartum)

• During pregnancy, the body accumulates 2000 to 3000 mL of excess fluid.
• This excess fluid leads to rapid bladder filling.
• Pressure from the fetal head on the bladder and urethra during vaginal birth can decrease bladder tone and sensory awareness of fullness.
• Frequent assessment of a woman's abdomen postpartally is essential to prevent bladder overdistention.

The Circulatory System (Postpartum)

• Average blood loss during vaginal birth is 300 to 500 mL, while Cesarean births typically result in 500 to 1000 mL blood loss.
• High levels of plasma fibrinogen persist in the first postpartum weeks, which helps prevent hemorrhage but increases the risk of blood clots.

The Gastrointestinal System (Postpartum)

• Digestion and absorption start working again soon after birth, except in women who have had a Cesarean birth.
• Postpartum women experience hunger and thirst and can eat without difficulty or nausea.
• Hemorrhoids may be present due to the physical strain of pushing during labor.
• Bowel sounds are active, but bowel movements may be delayed due to the effects of relaxin.
• Pain from episiotomy sutures or hemorrhoids can make bowel evacuation difficult.

The Integumentary System (Postpartum)

• Stretch marks (striae gravidarum) remain red and may even be more prominent after birth.
• Excessive pigmentation on the face, neck (chloasma), and abdomen (linea nigra) fades within 6 weeks.

Temperature (Postpartum)

• A slight increase in temperature within the first 24 hours after birth is common due to dehydration during labor.
• The timing of meconium passage in newborns can be an indicator of potential health issues. If a newborn does not pass meconium within the first 24 hours, it may suggest imperforate anus or meconium ileus.

Male Genitalia (Newborn)

• Typically, the scrotum is edematous with folds (rugae).
• Both testes should be present in the scrotum.
• Cryptorchidism: One or both testes not present requires referral.
• Agenesis: Absence of an organ.
• Ectopic Testes: The testes cannot enter the scrotum due to a closed opening.
• Undescended Testes: The vas deferens or artery is too short to allow the testes to descend.

Female Genitalia (Newborn)

• The vulva may be swollen due to maternal hormones.
• Pseudomenstruation: Mucus vaginal secretion, sometimes blood-tinged, caused by maternal hormones. Disappears as the infant's system clears the hormones. Not an infection or indication of trauma.

Back (Newborn)

• The spine appears flat in the lumbar and sacral areas.
• Adult-like spinal curves develop as the child sits and walks.
• Inspect the base of the spine for any pinpoint opening, dimpling, or sinus tract, which could suggest a dermal sinus or spinal bifida occulta.
• The incidence of neural tube defects in newborns has significantly decreased due to increased awareness about the importance of folic acid during pregnancy.

Extremities (Newborn)

• Arms and legs appear short.
• Hands are plump and clenched.
• Fingernails are soft, smooth, and often extend past fingertips.
• Fingertips should reach the proximal thigh.
• Unusually short arms may indicate achondroplastic dwarfism.
• Curvature of the little finger and a single palmar crease (simian crease) are common but can be associated with Down syndrome.
• Webbing (Syndactyly): Two or more digits fused together.
• Polydactyly: Extra toes or fingers.
• Newborn legs are bowed and short.