18 7.3 (4.6–11.6) 319 3.2 (1.9–5.0) incidence rate ratios (irrs) of first vte during pregnancy and the postpartum period swedish data a swedish data b english data danish data time period irr* (95% ci) irr* (95% ci) irr (95% ci)† irr (95% ci)† outside pregnancy reference (i.e., 1.00) antepartum 5.08 (4.66–5.54) 3.80 (3.44–4.19) 3.10 (2.63–3.66) 2.95 (2.68–3.25) trimester 1 3.42 (2.95–3.98) 3.04 (2.58–3.56) 1.46 (0.96–2.20) 1.12 (0.86–1.45) trimester 2 4.31 (3.78–4.93) 3.01 (2.56–3.53) 1.82 (1.27–2.62) 1.58 (1.24–1.99) trimester 3 7.14 (6.43–7.94) 5.12 (4.53–5.80) 5.69 (4.66–6.95) 5.48 (4.89–6.12) around delivery 37.5 (30.9–44.45) 27.97 (22.24–35.17) 44.5 (31.68–62.54) – postpartum 10.21 (9.27–11.25) 8.72 (7.83–9.70) 8.54 (7.16–10.19) 4.85 (4.21–5.57) early postpartum 19.27 (16.53–20.21) 15.62 (14.00–17.45) 14.61 (12.10–17.67) 8.44 (7.27–9.75) late postpartum 2.06 (1.60–2.64) 1.69 (1.26–2.25) 2.29 (1.44–3.65) 0.89 (0.53–1.39) notes: swedish data a = using any code for vte regardless of confirmation. swedish data b = using only algorithm-confirmed vte. early postpartum = first 6 weeks after delivery. late postpartum = more than 6 weeks after delivery. * = adjusted for age and calendar year. † = unadjusted ratio calculated based on the data provided. source: edema edema, or swelling, of the feet is common during pregnancy, partly because the enlarging uterus compresses veins and lymphatic drainage from the legs. metabolic during pregnancy, both protein metabolism and carbohydrate metabolism are affected. one kilogram of extra protein is deposited, with half going to the fetus and placenta, and another half going to uterine contractile proteins, breast glandular tissue, plasma protein, and haemoglobin. an increased requirement for nutrients is given by fetal growth and fat deposition. changes are caused by steroid hormones, lactogen, and cortisol. maternal insulin resistance can lead to gestational diabetes. increased liver metabolism is also seen, with increased gluconeogenesis to increase maternal glucose levels. body weight illustration of fundal height at various points during pregnancy some degree of weight gain is expected during pregnancy. the enlarging uterus, growing fetus, placenta, amniotic fluid, normal increase in body fat, and increase in water retention all contribute weight gain during pregnancy. the amount of weight gain can vary from 5 pounds (2.3 kg) to over 100 pounds (45 kg). in the united states, the range of weight gain that doctors generally recommend is 25 pounds (11 kg) to 35 pounds (16 kg), less if the woman is overweight, more (up to 40 pounds (18 kg)) if the woman is underweight. nutrition main article: nutrition and pregnancy nutritionally, pregnant women require a caloric increase of 350 kcal/day and an increase in protein to 70 or 75 g/day. there is also an increased folate requirement from 0.4 to 0.8 mg/day (important in preventing neural tube defects). on average, a weight gain of 20 to 30 lb (9.1 to 13.6 kg) is experienced. all patients are advised to take prenatal vitamins to compensate for the increased nutritional requirements. choline supplementation of research mammals supports mental development that lasts throughout life. renal and lower reproductive tract genitourinary changes in pregnancy progesterone causes many changes to the genitourinary system. a pregnant woman may experience an increase in the size of the kidneys and ureter due to the increase blood volume and vasculature. later in pregnancy, the woman might develop physiological hydronephrosis and hydroureter, which are normal. progesterone causes vasodilatation and increased blood flow to the kidneys, and as a result glomerular filtration rate (gfr) commonly increases by 50%, returning to normal around 20 weeks postpartum. the increased gfr increases the excretion of protein, albumin, and glucose. the increased gfr leads to increased urinary output, which the woman may experience as increased urinary frequency. 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. pregnancy alters the vaginal microbiota with a reduction in species/genus diversity. physiological hydronephrosis may appear from six weeks. gastrointestinal changes in the gastrointestinal (gi) system during pregnancy are caused by the enlarging uterus and hormonal changes of pregnancy. anatomically, the intestine and stomach are pushed up from their original positions by the enlarging uterus. while there aren't any intrinsic changes in the sizes of the gi organs, the portal vein increases in size due to the hyperdynamic state of pregnancy. elevated levels of progesterone and estrogen mediate most of the functional changes of the gi system during pregnancy. 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 increased occurrence of gallstones during pregnancy is due to inhibition of gallbladder contraction (as result of increased smooth muscle relaxation mediated by progesterone) and reduced biliary transportation of bile (mediated by estrogen) which results in cholestasis of pregnancy. nausea and vomiting of pregnancy, commonly known as morning sickness, is one of the most common gi symptoms of pregnancy. it begins between the 4 and 8 weeks of pregnancy and usually subsides by 14 to 16 weeks. 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. hyperemesis gravidarum, which is a severe form of nausea and vomiting of pregnancy can lead to nutritional deficiencies, weight loss, electrolytes imbalance and is one of the leading causes of hospitalization in the first trimester of pregnancy. constipation is another gi symptom that is commonly encountered during pregnancy. it is associated with the narrowing of the colon as it gets pushed by the growing uterus found adjacent it leading to mechanical blockade. reduced motility in the entire gi system as well as increased absorption of water during pregnancy are thought to be contributing factors. dietary cravings and dietary as well as olfactory avoidance of certain types of food are common in pregnancy. although the exact mechanisms of these symptoms are not fully explained, it is thought that dietary cravings may arise from the thought that certain foods might help relieve nausea. pica, which is the intense craving for unusual materials such as clay and ice has also been reported in pregnancy. hemorrhoids and gingival disease are two common pregnancy associated physical findings involving the gastrointestinal system. hemorrhoids arise as a result of constipation and venous congestion that are common in pregnancy. gingival disease is thought to be related to gum softening and edema (swelling from fluid collection) that is mostly observed in pregnancy. the mechanism and reason for the gingival changes are poorly understood. immune tolerance main article: immune tolerance in pregnancy the fetus inside a pregnant woman may be viewed as an unusually successful allograft, since it genetically differs from the woman. in the same way, many cases of spontaneous abortion may be described in the same way as maternal transplant rejection. musculoskeletal neuromechanical adaptations to pregnancy refers to the change in gait, postural parameters, as well as sensory feedback, due to the numerous anatomical, physiological, and hormonal changes women experience during pregnancy. such changes increase their risk for musculoskeletal disorders and fall injuries. musculoskeletal disorders include lower-back pain, leg cramps, and hip pain. pregnant women fall at a similar rate (27%) to women over age of 70 years (28%). most of the falls (64%) occur during the second trimester. additionally, two-thirds of falls are associated with walking on slippery floors, rushing, or carrying an object. the root causes for these falls are not well known. however, some factors that may contribute to these injuries include deviations from normal posture, balance, and gait. the body's posture changes as the pregnancy progresses. the pelvis tilts and the back arches to help keep balance. poor posture occurs naturally from the stretching of the woman's abdominal muscles as the fetus grows. these muscles are less able to contract and keep the lower back in proper alignment. the pregnant woman has a different pattern of gait. the step lengthens as the pregnancy progresses, due to weight gain and changes in posture. on average, a woman's foot can grow by a half size or more during pregnancy. in addition, the increased body weight of pregnancy, fluid retention, and weight gain lowers the arches of the foot, further adding to the foot's length and width. the influences of increased hormones such as estrogen and relaxin initiate the remodeling of soft tissues, cartilage and ligaments. certain skeletal joints such as the pubic symphysis and sacroiliac widen or have increased laxity. the addition of mass, particularly around the torso, naturally changes a pregnant mother's center of mass (com). the change in com requires pregnant mothers to adjust their bodies to maintain balance. lumbar lordosis to positionally compensate the additional load due to the pregnancy, pregnant mothers often extend their lower backs. 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. the arching of the lumbar region is known as lumbar lordosis, which recovers the center of mass into a stable position by reducing hip torque. according to a study conducted by whitcome, et al., lumbar lordosis can increase from an angle of 32 degrees at 0% fetal mass (i.e. non-pregnant women or very early in pregnancy) to 50 degrees at 100% fetal mass (very late in pregnancy). postpartum, the angle of the lordosis declines and can reach the angle prior to pregnancy. unfortunately, while lumbar lordosis reduces hip torque, it also exacerbates spinal shearing load, which may be the cause for the common lower back pain experienced by pregnant women. evolutionary implications given the demands of fetal loading during pregnancy and the importance of producing offspring to the fitness of human beings, natural selection may have had a role in selecting a unique anatomy for the lumbar region in females. there are sex differences in the lumbar vertebral column of human males and females, which ultimately helps mitigate some of the discomfort due to the fetal load in females. there are 5 vertebrae in the lumbar region for both males and females. however, the 3 lower vertebrae of a female's lumbar region are dorsally wedged while for males, only the lower 2 of the lumbar region are dorsally wedged. 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. if natural selection has acted on the lumbar region of homo sapiens to create this sexual dimorphism, then this sort of trait should also be apparent in the genus australopithecus, hominins that have been known to be habitually bipedal for at least 2 million years after the earliest bipedal hominins. currently there are 2 nearly complete australopith lumbar segments; one has three dorsally wedged vertebrae in the lumbar region while the other has two. an explanation for these findings is that the first one is a female, while the latter is a male. this sort of evidence supports the notion that natural selection has played a dimorphic role in designing the anatomy of the vertebral lumbar region. postural stability the weight added during the progression of pregnancy also affects the ability to maintain balance. perception pregnant women have a decreased perception of balance during quiet standing, which is confirmed by an increase in anterior-posterior (front to back) sway. this relationship heightens as pregnancy progresses and significantly decreases postpartum. to compensate for the decrease in balance stability (both actual and perceived), stance width increases to maintain postural stability. response to perturbations as measured by a force platform, parameters used to measure postural stability. adapted from mccrory et al. 2010 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. initial sway, total sway, and sway velocity (see figure for description of variables) are significantly less during the third trimester than during the second trimester and when compared to non-pregnant women. these biomechanical characteristics are possible reasons why falls are more prevalent during the second trimester during pregnancy. additionally, the time it takes for pregnant women (any stage of pregnancy) to react to a translational disturbance is