Maternal physiological changes in pregnancy

Pregnant women experience numerous adjustments in their endocrine system that help support the developing fetus.

The fetal-placental unit secretes steroid hormones and proteins that alter the function of various maternal endocrine glands.

Levels of progesterone and estrogen rise continually throughout pregnancy, suppressing the hypothalamic axis and subsequently the menstrual cycle.

[3] The placenta also produces human placental lactogen (hPL), which stimulates maternal lipolysis and fatty acid metabolism.

Prolactin mediates a change in the structure of the breast mammary glands from ductal to lobular-alveolar and stimulates milk production.

The adrenal gland also produces more androgens, such as testosterone, but this is buffered by estrogen's increase in sex-hormone binding globulin (SHBG).

Once full lactation begins, the woman's breasts swell significantly and can feel achy, lumpy and heavy (which is referred to as engorgement).

[19][20] Breast size does not determine the amount of milk a woman will produce or whether she will be able to successfully breastfeed her baby.

Overall, the systolic and diastolic blood pressure drops 10–15 mm Hg in the first trimester and then returns to baseline in the second half of pregnancy.

[6] Uterine enlargement beyond 20 weeks' size can compress the inferior vena cava, which can markedly decrease the return of blood into the heart or preload.

As a result, healthy pregnancy patients in a supine position or prolonged standing can experience symptoms of hypotension.

[24] Due to dilution, the net result is a decrease in hematocrit or hemoglobin, which are measures of red blood cell concentration.

[24] The slight drop in hematocrit or hemoglobin is most pronounced at the end of the second trimester and slowly improves when reaching term.

[28] Many factors have been shown to increase the risk of clots in pregnancy, including baseline thrombophilia, cesarean section, preeclampsia, etc.

[30] Edema, or swelling, of the feet is common during pregnancy, partly because the enlarging uterus compresses veins and lymphatic drainage from the legs.

Progesterone also causes decreased motility of the ureters, which can lead to stasis of the urine and hence an increased risk of urinary tract infection.

Progesterone causes smooth muscle relaxation which slows down GI motility and decreases lower esophageal sphincter (LES) tone.

The resulting increase in intragastric pressure combined with lower LES tone leads to the gastroesophageal reflux commonly experienced during pregnancy.

The exact cause of nausea is not fully understood but it correlates with the rise in the levels of human chorionic gonadotropin, progesterone, and the resulting relaxation of smooth muscle of the stomach.

Reduced motility in the entire GI system as well as increased absorption of water during pregnancy are thought to be contributing factors.

Gingival disease is thought to be related to gum softening and edema (swelling from fluid collection) that is mostly observed in pregnancy.

As the fetal load increases, women tend to arch their lower backs, specifically in the lumbar region of their vertebral column to maintain postural stability and balance.

Unfortunately, while lumbar lordosis reduces hip torque, it also exacerbates spinal shearing load,[39] which may be the cause for the common lower back pain experienced by pregnant women.

When a female arches her lower back, such as during fetal loading, having an extra dorsally wedged vertebra lessens the shearing force.

This lumbar sexual dimorphism in humans suggests high natural selection pressures have been acting to improve maternal performance in posture and locomotion during pregnancy.

This sort of evidence supports the notion that natural selection has played a dimorphic role in designing the anatomy of the vertebral lumbar region.

Pregnant women have a decreased perception of balance during quiet standing, which is confirmed by an increase in anterior-posterior (front to back) sway.

Under dynamic postural stability, which can be defined as the response to anterior (front) and posterior (back) translation perturbations, the effects of pregnancy are different.

While the idea of "waddling" cannot be dispensed, these results suggest that exercise and conditioning may help relieve these injuries.

The combined effect of the decreased serum concentrations of both carbon dioxide and bicarbonate leads to a slight overall increase in blood pH (to 7.44 compared to 7.40 in the non-pregnant state) .