Physiology, Postpartum Changes

Gaurav Chauhan; Prasanna Tadi

Physiology, Postpartum Changes

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Introduction

The postpartum period is the period after delivery of conceptus when maternal physiological and anatomical changes return to the nonpregnant state. The postpartum period, also known as puerperium, starts following the expulsion of the placenta until complete physiological recovery of various organ systems. The postpartum period is divided into 3 arbitrary phases, ie, the acute phase - the first 24 hours after delivery of the placenta; early – up to 7 days; and late – up to 6 weeks to 6 months. Each phase has its unique clinical considerations and challenges.[1][2]

Organ Systems Involved

General Physiological Changes

There is generalized physical fatigue immediately after delivery. The pulse rate may be elevated a few hours after childbirth due to excitement or pain and usually normalizes on the second day. The blood pressure could be elevated due to pain or excitement but is generally in the normal range.[3] A significant decrease (> 20% below baseline) in blood pressure could be a sign of postpartum hemorrhage or septic shock.[4] Conversely, high blood pressure could be a sign of pain or pre-eclampsia.[5] The temperature is slightly elevated up to 37.2C (99F) along with increased shivering, sweating, or diaphoresis in the first 24 hours and normalizes within 12 hours.[3][6] The rise in temperature is attributable to the systemic absorption of metabolites accumulated due to muscle contractions. There could be a transient temperature rise (by 0.5C) on the third or fourth day due to breast engorgement. The respiratory rate also begins to fall back to the pre-pregnancy level within 2 to 3 days. A rise in temperature beyond the third day or over the upper limit is usually a sign of infection.[7][8][9][7] A weight loss of 5 to 6 kg due to the expulsion of products of gestation and accompanying blood loss. Further weight loss of 2 to 3 kg can be attributed to the brisk diuresis. The weight loss due to diuresis may continue up to 6 months after delivery.

Reproductive

Involution, a part of postpartum physiology, refers to the process of reproductive organs returning to their prepregnant state. Immediately following the delivery, the uterus and the placental site contract rapidly to prevent further blood loss. This rapid uterine contraction can lead to abdominal pain or cramps after childbirth. At this point, the uterus has an increased tone, feels firm, and weighs 1000 gms. at the end of the first week, it weighs 500 gms, and by 6 weeks, it weighs approximately 50 gms. The female may complain. Initially, the contraction of the uterus is due to a substantial reduction in myometrial cell size; it constricts the blood vessels and limits the bleeding. The subsequent decrease in size is due to autolysis and infarction of uterine blood vessels.[10][11][12] The withdrawal of estrogen and progesterone leads to an increase in the activity of uterine collagenase and other proteolytic enzymes, accelerating the process of autolysis.[13] The intima and elastic tissues in the uterine blood vessels also undergo fibrosis and hyaline degeneration, leading to infarction and shedding of more uterine cells, which are removed by macrophages. The superficial and basal layers of the endometrium become necrotic and sloughed.[14] The endometrium is usually fully restored within 2 to 3 weeks.[15] The lochia is the vaginal discharge that originates from the uterus, cervix, and vagina. The lochia is initially red and comprises blood and fragments of decidua, endometrial tissues, and mucus. It lasts 1 to 4 days. The lochia then changes color to yellowish or pale brown, lasting 5 to 9 days, and is comprised mainly of blood, mucus, and leucocytes. Finally, the lochia is white and contains mostly mucus, lasting up to 10 to 14 days. The lochia can persist up to 5 weeks postpartum. The persistence of red lochia beyond 1 week might indicate uterine subinvolution. The presence of an offensive odor or large pieces of tissue or blood clots in lochia or the absence of lochia might be a sign of infection.[16][17][18] The cervix and vagina may be edematous and bruised in the early postpartum period and gradually heal back to normal.[19] Once the ovarian function resumes, rugae start to appear in the vagina, usually by the third week in females that are not breastfeeding. Similarly, the postpartum vaginal epithelium, which appears atrophic under the microscopic exam, is restored in 6 to 10 weeks, but the recovery delays in breastfeeding females due to low estrogen levels. The patient may develop perineal edema, lacerations, tears, or undergo an episiotomy in the immediate postpartum period that may lead to discomfort and pain.[20][21]

Lactation

The secretion from the breasts, called colostrum, increases after childbirth. Colostrum is rich in protein, vitamins, immunoglobulins, and other humoral factors (lactoferrin) and provides an immunological defense to the newborn.[22] The mammogenesis or preparation of breasts for lactation starts during pregnancy and entails ductal and lobuloalveolar hyperplasia and hypertrophy.[23] The high levels of estrogen and progesterone make the breast tissue unresponsive to prolactin. Still, as their levels decrease dramatically following childbirth, the prolactin begins its milk secretory activity in the mammary glands. The lactogenesis or milk secretion starts on the third or fourth day postpartum. The neural arch of lactation involves ascending afferent impulses from the nipple and areola, activated by suckling or stimulation of nipples, which pass via thoracic sensory nerves to the paraventricular and supraoptic nuclei of the hypothalamus, promoting the synthesis and secretion of Oxytocin from the posterior pituitary. Oxytocin affects the contraction of myoepithelial cells, leading to galactokinesis or milk expression from the mammary ducts. This release is also known as "milk ejection" or milk let down reflex." The milk ejection reflex can be inhibited by pain, anxiety, depression, breast engorgement, or depression. Prolactin maintains galactopoiesis, which is defined as the maintenance of effective and continuous lactation. A healthy mother secretes 500-800 ml of milk daily, which requires 700kcal/ day. The fat stores of up to 5 kg gained during pregnancy can provide enough calories to compensate for any nutritional deficit during lactation. It is not unusual to develop nipple soreness or mastitis during this phase.[24][25]

Endocrine

The onset of the first menstrual period following delivery is variable and depends on whether the mother is lactating. If the mother is not breastfeeding, the menstrual function, in most cases, returns by the sixth to eighth week postpartum. The duration of anovulation depends on the frequency and intensity of breastfeeding and is attributed to high serum prolactin levels associated with suckling.[24] Elevated serum prolactin levels inhibit the ovarian response to the follicular stimulating hormone, suppress the release of luteinizing hormone, and suppress the secretion of gonadotropins even further. This approach offers a natural method of contraception to the lactating female. In lactating females, menstruation usually reappears in 4 to 5 months and, in some cases, can be as late as 24 months. However, ovulation can commence in the absence of menstruation, and pregnancy can occur.[25][26][27] Non-lactating mothers should use contraceptive measures after 3 weeks and lactating mothers after 3 months of delivery.[28] The level of human chorionic gonadotropin that mimics stimulating thyroid hormone falls dramatically after delivery. Consequently, the thyroid gland volume regresses to the pre-pregnant state by 12 weeks, and the thyroid function returns to normal by 4 weeks postpartum.[29][30] The diabetogenic effects of pregnancy are due to the production of placental insulinase, corticotropin-releasing hormone, and human placental lactogen.[31] The insulin sensitivity increases after delivery and is restored within 2 to 3 days.[32] However, in obese females, postpartum normalization of insulin sensitivity may take 15 to 16 weeks.[33]

Renal

The bladder wall may become edematous and hyperemic, and the bladder might be overdistended without the urge to pass urine.[34] The retention of urine in the first few days after labor may be due to the laxity of the abdominal musculature, tone of pelvic floor muscles, atony of bladder, compression of urethra by edema or hematoma, reflex inhibition of micturition due to genitourinary trauma.[35][1][35] Conversely, urinary incontinence, especially urge incontinence, affects 30% of postpartum females and is attributed most commonly to psychological stress associated with childbirth.[36] The mother may complain of painful micturition or dysuria that could be due to tears, laceration of the cervix or vagina, or episiotomy. During pregnancy, the compressive forces of the gravid uterus and the progesterone-induced decrease in ureteral tone, peristalsis, and contraction pressure lead to the dilation of the calyceal system, increasing the volume of kidneys by 30% from the pre-pregnant state.[37][38][37] The dilated ureters and renal pelvis usually return to the pre-pregnant state within 4-8 weeks. There is an increased risk of developing urinary tract infections. It is important to counsel the mother to void every 3 to 4 hours.[39]

Fluids

A fluid shift from extravascular to intravascular space corresponds to 6 to 8 liters of total body water. Furthermore, the persistent activity of the renin-angiotensin-aldosterone system during pregnancy leads to an excess of 950 mEq of sodium.[40] In the postpartum period, there are increased serum levels of the atrial natriuretic peptide (1.5 times normal) that inhibits aldosterone, angiotensin II, and vasopressin and promotes urinary sodium excretion. There is brisk diuresis in the first 2 weeks after childbirth, and it is not uncommon to have a urinary output of 3000 cc/day. The loss is usually in line with the fluid retained during pregnancy. The glomerular filtration rate returns to baseline at 8 weeks postpartum.[39] Lactosuria is not uncommon on the third or fourth day of the start of lactation.[41]

Hematologic

The hematocrit may initially drop due to blood loss associated with delivery but starts to rise again plasma volume decreases due to diuresis and hemoconcentration.[42] The hematocrit values return to normal in 3-5 days postpartum as plasma volume increases. The discrepancy in hemoglobin values in the postpartum phase is due to the variability in the plasma volume due to fluid shifts. Studies evaluating the longitudinal hemoglobin values in the postpartum phase indicate that it takes at least 4-6 months to restore the pregnancy-induced dip in hemoglobin to non-pregnant states.[43] The patient may develop leucocytosis (approximately 25,000/mm³) due to the stress associated with labor. The white blood cell count returns to pre-pregnant values within 4 weeks.[44] The gestational thrombocytopenia resolves 4 to 10 days after delivery as platelet count increases in response to platelet consumption during delivery.[44][45] During pregnancy, the fibrinogen, factor VII, VIII, X, XII, von Willebrand factor, and ristocetin activity increase significantly as gestation progresses to prepare for delivery and prevent excess blood loss.[46] In the early postpartum period, the fibrinogen levels are still high, and platelets begin to rise to normal values. The tissue plasminogen, an enzyme responsible for clot lysis, doesn't rise or normalize in the early postpartum period. During pregnancy, the hypercoagulable state resolves gradually after birth, as clotting factor levels normalize in 8 to 12 weeks postpartum.[47][48] The changes in the coagulation system confer an increased risk for thromboembolic phenomena that are approximately ten-fold during pregnancy and twenty-fold during the early postpartum period.[49][50] Furthermore, the in vitro tests to assess or predict the possibility of thromboembolism, such as d-dimer tests and fibrin degradation products assay, are less reliable in the immediate postpartum period.[51]

Cardiovascular

Significant structural and hemodynamic alterations occur during the peripartum period. Cardiac output increases throughout pregnancy. However, in the immediate postpartum period, following delivery, there is an increase in circulating blood volume from the contraction of the uterus and an increase in preload from the relief of inferior vena cava obstruction, leading to an increase in stroke volume and heart rate leading to a 60 to 80% rise in cardiac output, which rapidly declines to pre-labor values in 1 to 2 hours following delivery and to pre-pregnancy values in 2 weeks postpartum.[52][53] Increased serum levels of progesterone and relaxin, a peptide hormone produced by the corpus luteum and placenta, promote systemic vasodilation, leading to a progressive decrease in systemic vascular resistance (SVR). SVR decreases by 35 to 40% during pregnancy and increases to pre-pregnant levels in 2 weeks postpartum. There is also a decrease in systemic blood pressure by 5 to 10 mm Hg during pregnancy. Diastolic blood pressure decreases more than systolic blood pressure. The systemic blood pressures rise during the third trimester and return to prepregnant values at 16 weeks postpartum.[54] Heart rate increases linearly during pregnancy by 10 to 20 bpm over baseline and returns to pre-pregnant levels 6 weeks postpartum.[55][55] There is ventricular remodeling during pregnancy and left ventricular wall thickness and mass increase by 28% to 52% above pre-pregnancy values. A few recent studies also report an increase in right ventricular volume and mass by 40% during pregnancy. The physiological hypertrophy of the ventricular system reverts to the pre-pregnant state in 4 weeks postpartum.[56][57] Cardiac contractility and ventricular ejection fraction don't significantly change during the entire peripartum period.[55]

Gastrointestinal

The mother may develop flatulence or constipation due to intestinal ileus (induced by pain or the presence of placental hormone relaxin in the circulation), loss of body fluids, laxity of the abdominal wall, and hemorrhoids.[58][59] The postpartum constipation is due to the progesterone-induced decrease in gastrointestinal transit time.[58] The compressive effects of the gravid uterus on the stomach, a decrease in lower esophageal sphincter tone due to high progesterone levels, and hypersecretion of acid due to high gastrin levels cause an increase in the incidence of acid reflux during pregnancy. After delivery, the levels of progesterone and gastrin drop within 24 hours, and the acid reflux and associated symptoms resolve in the next 3 to 4 days.[60][61][62][63]

Integumentary

Hyperpigmentation is the most commonly reported skin change during pregnancy, affecting 85% to 90% of females.[64] The hypothesis is that melanocytes are sensitive to elevated estrogen, progesterone, and endorphin levels during pregnancy. Humoral factors produced by the placenta lead to the upregulation of tyrosine kinase, promoting further melanin synthesis.[65][66] The pigment changes accompanying pregnancy (melasma and linea nigra) usually disappear by 6 to 8 weeks.[67] Elevated estrogen during pregnancy can lead to telangiectasis and spider angiomata.[68] Venous dilation and increased hydrostatic pressure due to the gravid uterus can lead to nonpitting edema and varicosities in the lower extremities, which returns to baseline in the postpartum period.[69] The nails undergo symmetrical, uniform hyperpigmentation during pregnancy that fades away postpartum.[70] The abdominal muscles are overstretched during pregnancy and strained during labor and are slow to regain their normal tone and elasticity, returning to pre-pregnancy levels by 6 to 8 weeks. The patient may have divarication of recti, and the striae or stretch marks over the abdomen and legs might not disappear.[66]

Clinical Significance

Human physiology is significantly altered during pregnancy and in the postpartum period. The physician should know the physiological changes associated with the postpartum period. The clinician should be able to tell the difference between healthy and abnormal to effectuate a diagnostic and therapeutic algorithm, especially in cases of acute emergencies such as postpartum hemorrhage, sepsis, amniotic fluid embolism, or uterine inversion. Furthermore, one should be aware of the hormonal changes related to the puerperium and lactation to formulate an effective contraception plan in the postpartum period. Thromboprophylaxis in the postpartum period is a constant topic of debate due to the high incidence of venous thromboembolism in the postpartum period, and females are risk-stratified into low-risk, medium-risk, and high-risk. Females with no coagulation anomalies or low-risk history don't require any thromboprophylaxis. Intermediate-risk females should be instituted thromboprophylaxis after delivery of up to 7 days of puerperium. The females that are high risk receive thromboprophylaxis throughout pregnancy and up to 7 days of postpartum. The conduct of anesthesia for surgery also varies according to the timeline post-delivery. Patients undergoing surgery under general anesthesia within 48 hours of delivery should be treated with a full stomach. They should receive anti-aspiration measures, including non-particulate antacids and rapid sequence induction of anesthesia.

Details

References

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