Physiological adaptations to pregnancy

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Lecture 2 - 2004

• Physiological adaptations to pregnancy
• Psychology
• Energy
• Weight Gain

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Physiology of Pregnancy
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Systematic Adjustments to Pregnancy

• Cardiovascular
• Respiratory
• Urinary

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Cardiac output during three stages of gestation,
labor, and immediately postpartum compared with
values of nonpregnant women. All values were
determined with women in the lateral recumbent
position.
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Change in cardiac outline that occurs in
pregnancy. The light lines represent the
relations between the heart and thorax in the
nonpregnant woman, and the heavy lines represent
the conditions existing in pregnancy. These
findings are based on x-ray findings in 33 women.
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TABLE 8-4. Ventilatory Function in Pregnant Women Compared with the Postpartum Period TABLE 8-4. Ventilatory Function in Pregnant Women Compared with the Postpartum Period TABLE 8-4. Ventilatory Function in Pregnant Women Compared with the Postpartum Period TABLE 8-4. Ventilatory Function in Pregnant Women Compared with the Postpartum Period TABLE 8-4. Ventilatory Function in Pregnant Women Compared with the Postpartum Period
  During Pregnancy During Pregnancy During Pregnancy
Factor 10 Weeks 24 Weeks 36 Weeks Postpartum6-10 Weeks
Respiratory rate 15-16 16 16-17 16-17
Tidal volume (mL) 600-650 650 700 550a
Minute ventilation (L) 10.5 7.5a
Vital capacity (L) 3.8 3.9 4.1 3.8
Inspiratory capacity (L) 2.6 2.7 2.9 2.5
Expiratory reserve volume (L) 1.2 1.2 1.2 1.3
Residual volume (L) 1.2 1.1 1.0 1.2a
a Significant increase or decrease compared with pregnant women. a Significant increase or decrease compared with pregnant women. a Significant increase or decrease compared with pregnant women. a Significant increase or decrease compared with pregnant women. a Significant increase or decrease compared with pregnant women.



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Mean glomerular filtration rate in healthy women
over a short period with infused inulin (solid
line), simultaneously as creatinine clearance
during the inulin infusion (broken line), and
over 24 hours as endogenous creatinine clearance
(dotted line).
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King J. Physiology of pregnancy and nutrient
metabolism. Am J Clin Nutr 200071
(suppl)1218S-25S
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Adjustments in Nutrient Metabolism

• Goals
• support changes in anatomy and physiology of
  mother
• support fetal growth and development
• maintain maternal homeostasis
• prepare for lactation
• Adjustments are complex and evolve throughout
  pregnancy

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General Concepts

• 1. Alterations include
• increased intestinal absorption
• reduced excretion by kidney or GI tract
• 2. Alterations are driven by
• hormonal changes
• fetal demands
• maternal nutrient supply

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• 3. There may be more than one adjustment for each
  nutrient.
• 4. Maternal behavioral changes augment
  physiologic adjustments
• 5. When adjustment limits are exceeded, fetal
  growth and development are impaired.

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Birth weight of 11 children born to a poor woman
in Montreal 8 children were born before
receiving nutritional counseling and food
supplements from the Montreal Diet Dispensary and
3 children were born afterward.
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• 6. The first half of pregnancy is a time of
  preparation for the demands of rapid fetal growth
  in the second half

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Hormonal Adjustments

• Estrogens increase significantly in pregnancy,
  influence carbohydrate, lipid, and bone
  metabolism
• Progesterone relaxes smooth muscle and causes
  atony of GI and urinary tract
• Human Placental Lactogen (hPL) stimulates
  maternal metabolism, increases insulin
  resistance, aids glucose transport across
  placenta, stimulates breast development

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Late gestation is characterized by

• Anti-insulinogenic and lipolytic effects of Human
  chorionic somatomammotropin, prolactin, cortisol,
  glucagon)
• Which Results in
• Glucose intolerance, insulin resistance,
  decreased hepatic glycogen, mobilization of
  adipose tissue

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Mean (SEM) plasma lipid concentrations (mg/dL)
throughout gestation (n 42) and during the
luteal (I) and follicular (II) phases postpartum
(p.p. n 23). The dashed lines represent the
mean values of the control group (n 24). (FC
free cholesterol PL phospholipids TC total
cholesterol TG triglycerides.)(
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Maternal Nutrient Levels

• Increased triglycerides
• Increased cholesterol
• Decreased plasma amino acids albumin
• Plasma volume increases 40 (range 30-50)
• nutrient concentration declines due to increased
  volume, but total amount of vitamins and minerals
  in circulation actually increases.

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Mean hemoglobin concentrations (    ) and 5th
and 95th (    ) percentiles for healthy
pregnant women taking iron supplements
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Maternal Nutrient Levels
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Nitrogen Balance (g/day)
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Alterations in maternal physiology facilitate
transfer of nutrients to the fetus.
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Nutrient Transportation Across The Placenta
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Factors Affecting Placental Transfer

• Diffusion distance - diabetes and infection cause
  edema of the villi
• Maternal-placental blood flow
• Blood saturation with gases and nutrients
• Maternal-placental metabolism of the substance

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Psychology of Pregnancy

• Psychosocial tasks
• Rubin
• Leadermans tasks
• Fathers
• Cultural awareness

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Developmental Tasks of Pregnancy (Rubin, 1984)

• Seeking safe passage for herself and her child
  through pregnancy, labor, and delivery.
• Ensuring the acceptance by significant persons in
  her family of the child she bears.
• Binding-in to her unknown baby.
• Learning to give of herself.

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Lederman, RP. Psychosocial Adaptation in
Pregnancy, 2nd Ed. 1996

• Developmental Tasks of Pregnancy
• acceptance of pregnancy
• identification with motherhood role
• relationship to the mother
• relationship to the husband/partner
• preparation for labor
• processing fear of loss of control loss of self
  esteem in labor

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Psychosocial adjustment during pregnancy the
experience of mature gravidas (Stark, JOGNN, 1997)

• N64 older gravidas (gt 35), 46 younger gravidas
  (lt 32) in third trimester
• Lederman prenatal self evaluation questionnaire -
  examines conflicts for 7 steps
• In general conflicts about maternal role were
  similar in both groups
• Older gravidas had less concern about fear of
  helplessness and loss of control in labor -
  regardless of parity

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Developmental Tasks of Fatherhood

• Accepting the pregnancy
• Identifying the role of father
• Reordering relationships
• Establishing relationship with his child
• Preparing for the birth experience

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Laboring for Relevance Expectant and New
Fatherhood (Jordan, Nursing Research, 1990)

• N56 expectant fathers followed prospectively
• Tasks
• grappling with the reality of the pregnancy and
  child
• struggling for recognition as a parent from
  mother, coworkers, friends, family baby and
  society
• plugging away at the role-making of involved
  fatherhood

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Jordan, cont.

• Identified concerns
• Men not recognized as parents but as helpmates
  and breadwinners
• Men felt excluded from childbearing experience by
  mates, health care providers, and society
• Fathers felt that they had no role models for
  active and involved parenthood

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Energy Requirements in Pregnancy

• Energy costs of pregnancy
• increased maternal metabolic rate
• fetal tissues
• increase in maternal tissues

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RDA for Energy in Pregnancy - Old

• Energy cost of pregnancy 80,000 kcal (Hytten
  and Leitch, 1971)
• maternal gain of 12.5 kg
• infant weight of 3.3 kg
• 80,000/250 days (days after the first month)
• Additional 300 kcal per day recommended in second
  and third trimester
• total of 2,500 for reference woman

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DRI for Energy - New
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Estimated Energy Requirement

• Average dietary energy intake that is predicted
  to maintain energy balance in a healthy adult of
  a defined age, gender, weight, height, level of
  physical activity consistent with good health.
• In children, pregnant and lactating women the EER
  is taken to include the needs associated with
  deposition of tissues or secretion of milk

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DRI for Energy in Pregnancy - 2002
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BEE Basal Energy Expenditure

• Increases due to metabolic contribution of uterus
  and fetus and increased work of heart and lungs.
• Variable for individuals

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Growth of Maternal and Fetal Tissues

• Still based on work of Hytten
• Based on IOM weight gain recommendations

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Longitudinal Data from DLW Database

• Median TEE (total energy expenditure) change from
  non-pregnant was 8 kcal/gestational week.
• TEE changes little in first trimester.

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Variations in Energy Requirements

• Body size - especially lbm
• Activity
• most women decrease activity in last months of
  pregnancy if they can
• increased energy cost of moving heavier body
• BMR
• rises in well nourished women (27)
• rises less or not at all in women who are not
  well nourished
• -Diet Induced Thermogenesis?

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Evidence of energy sparing in Gambian women
during pregnancy a longitudinal study using
whole-body calorimetry (AJCN, 1993)

• N58, initially recruited, ages 18-40
• 25 became pregnant
• 21 participated in study protocols
• 9 completed BMR and 24 hour energy expenditure
• 12 completed BMR
• Adjusted for seasonality, weight loss expected
  during wet season

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Poppitt et al., cont.

• Mean maternal prepregnancy weight was 52 kg
• Mean prepregnancy BMI was 21.2 2
• Mean birthweight was 3.0 0.1
• Mean gestational length was 39.4
• Mean weight gain was 6.8 kg
• Mean fat gain was 2.0 kg at 36 weeks

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Poppitt et al., cont.

• BMR fell in early pregnancy
• Values per kg lbm remained below baseline for
  duration of pregnancy
• Individual variation was high

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Poppitt et al., cont.

• Energy sparing mechanisms may act via a
  suppression of metabolism in women on habitually
  low intakes.
• This maintains positive balance in the mother and
  protects the fetus from growth retardation

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• Prentice and Goldberg. Energy Adaptations in
  human pregnancy limits and long-term
  consequences. Am J Clin Nutr.
  200071(supple)1226S-32S.

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Longitudinal assessment of energy balance in
well-nourished, pregnant women (Koop-Hoolihan et
al, AJCN, 1999)

• N16, SF area
• 10 became pregnant
• BMI range was 19-26
• Mean weight gain at 36 weeks was 11.6 4
• Mean birth weight was 3.6

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Koop-Hoolihan, cont

• Protocol 5 times before pregnancy, 3 times
  during, once 4-6 weeks postpartum
• RMR (resting metabolic rate/metabolic cart)
• DIT (diet induced thermogenesis/metabolic cart)
• TEE (total energy expenditure/doubly labeled
  water)
• AEE (activity energy expenditure/difference
  between TEE and RMR)
• EI (energy intake/3 day food records)
• Body composition - densitometry, tbw, bmc with
  absorptiometry

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Koop-Hoolihan, cont

• Women with the largest cumulative increase in RMR
  deposited the least fat mass (this was the only
  prepregnant factor that predicted fat mass gain)
• In all indices there was large individual
  variation
• Average total energy cost of pregnancy was
  similar to work of Hytten and Leitch (1971)
• Food intake records indicated 9 increase in
  kcals with pregnancy, but highly variable

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Energy in Pregnancy (Roy Pitkin, AJCN, 1999)

• Koop-Hoolihan study design was Impeccable.
• Women meet increase energy demands of pregnancy
  in a variety of ways - increased intakes,
  decreased activity or DIT, limited fat storage.
• RDA?

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Energy in Pregnancy (Roy Pitkin, AJCN, 1999)

• A prudent course seems to be to permit
  considerable latitude in energy intake
  recommendations on the basis of individual
  preferences and to monitor weight gain carefully,
  making adjustments in energy intake only in
  response to the normal pattern of gain.

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Maternal Obesity

• Rates of obesity are increasing world-wide
• Obesity before pregnancy is associated with risk
  of several adverse outcomes

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Prepregnancy weight and the risk of adverse
pregnancy outcomes (Cnattingius et al, NEJM, 1998)

• N167,750 in Sweden, Norway, Finland, or Iceland
  who gave birth to singleton babies in 1992 and
  1993.
• Outcome late fetal death
• Adjusted for maternal age, parity, education,
  smoking, height and living with father

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Prepregnancy weight and the risk of adverse
pregnancy outcomes (Cnattingius et al, NEJM, 1998)
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Prepregnancy weight and the risk of adverse
pregnancy outcomes (Cnattingius et al, NEJM, 1998)
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Cnattingius et al, Discussion

• Even lean women were probably well nourished in
  this cohort. Results in other countries may be
  different.
• Maternal overweight may be major factor in SES
  differences in perinatal morbidity and mortality
• Impetus toward developing strategies to reverse
  trends toward increasing body weight

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Perinatal Outcomes of Obese Women A Review of
the Literature (Morin, JOGNN, 1998)

• Extensive Review of Medine and CINAHL
• Definitions of obesity vary, but IOM says obesity
  BMI gt 29

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Diagnosis

• Menses tend to be irregular and pelvic exams and
  ultrasound exams may be difficult
• AFP values may be lower than norms due to
  increased plasma volume
• Blood pressure monitoring may be difficult

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Antepartum Outcomes

• Higher rates of NTD even with folic acid
  supplementation (RR 3.0 in one study)
• Increased risk for both chronic and pregnancy
  induced hypertension
• Increased risk for severe preeclampsia (BMI lt
  32.3, risk was 3.5 times that of controls)
• Increased risk for both GDM, IDD and NIDD.
• Increased twining
• Increased UTI

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Labor and Birth Outcomes

• Increased incidence of both primary (31 vs 8.6)
  and secondary cesarean births - often associated
  with fetal macrosomia and/or failed induction.
• Operative times are longer
• Increased incidence of blood loss during surgery
• ? Differences in responses to anesthesia (greater
  spread/higher levels)

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Postpartum Outcomes

• Increased risk for wound and endometrial
  infection
• Increased prevalence of urinary incontinence

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Infant Outcomes

• Large infants - effect is independent of maternal
  diabetes
• Increased infant mortality - RR for infants born
  to obese women was 4.0 compared to women with BMI
  lt 20

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Cost

• Costs were 3.2 times higher for women with BMI gt
  35
• Longer hospitalizations

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Maternal Obesity and Pregnancy Outcomes Castro
Alvina, Curr Opin obstet Gynecol, 2002
Increased Risk in Obese Women
Pre-eclampsia 2 to 4 times as high
Diabetes 3 times as high
Postpartum hemorrhage 70 increase
Infant shoulder dystocia 2 times as high
Thromboembolic disease
Respiratory complications
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IOM Recommendations

• Institute of Medicine. Nutrition during
  pregnancy, weight gain and nutrient supplements.
  Report of the Subcommittee on Nutritional Status
  and Weight Gain during Pregnancy, Subcommittee on
  Dietary Intake and Nutrient Supplements during
  Pregnancy, Committee on Nutritional Status during
  Pregnancy and Lactation, Food and Nutrition
  Board. Washington, DC National Academy Press,
  1990

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Recommended total weight gain in pregnant women
by prepregnancy BMI (in kg/m2) Weight-for-height
category Recommended total gain (kg) Low (BMI
lt19.8) 12.518 Normal (BMI 19.826.0) 11.516
High (BMI gt26.029.0)2 711.5 Adolescents and
black women should strive for gains at the upper
end of the recommended range. Short women (lt157
cm) should strive for gains at the lower end of
the range. The recommended target weight gain for
obese women (BMI gt29.0) is 6.0.
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Cogswell M, Serdula M, Hungerford D, Yip R.
Gestational weight gain among average-weight and
overweight womenwhat is excessive? Am J Obstet
Gynecol 199517270512
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Incidence of adverse outcomes for 6690
pregnancies in San Francisco
Parker J, Abrams B. Prenatal weight gain advice
an examination of the recent prenatal weight gain
recommendations of the Institute of Medicine.
Obstet Gynecol 1992796649
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Percentage of US women with normal prepregnancy
weights who retained gt9 kg 1024 mo postpartum
relative to prepregnancy weight
(Parker J, Abrams B. Differences in postpartum
weight retention between black and white mothers.
Obstet Gynecol 19938176874)
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Rates of Weight Gain T2 and T3

• Underweight women 0.5 kg per week
• Normal weight women 0.4 kg per week
• Overweight women 0.3 kg per week

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Postpartum Weight

• IOM (1990) concluded that childbearing is
  associated with average weight gain of 1kg.
• There is a large variation in differences between
  prepregnant weight and weight at 6 to 12 months
  postpartum (SD of 4.8 kg)
• Analysis is confused by the tendency to gain
  weight with aging
• Years between 25 and 34 are times when American
  women are most vulnerable to major weight gain

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Postpartum Weight

• Proportions of black women who have higher
  postpartum weights is higher in almost all
  studies.
• Smoking is consistently related to less
  postpartum weight gain.

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Predictors of weight gain at 6 and 18 months
after childbirth a pilot study (Walker, JOGNN,
1996)

• N88 at 6 months, 75 at 18 months
• Out of about 300 who were sent a mailed
  questionnaire 6 and 18 months postpartum
• Predominantly white mothers in the Midwestern US

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Predictors of weight gain at 6 and 18 months
after childbirth a pilot study (Walker, JOGNN,
1996)

• Battery of tests including
• Health promoting lifestyle profile (48 items on
  exercise, nutrition, support self-actualization)
• Categories of activity level
• Weight locus of control scale (internal or
  external)
• Self reported weight and height, method of
  delivery, method of infant feeding

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Predictors of weight gain at 6 and 18 months
after childbirth a pilot study (Walker, JOGNN,
1996)
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Walker, Results

• At both 6 and 18 months, women who exceeded IOM
  wt. Gain recommendations had significantly higher
  pp weight increases.

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Sociocultural and behavioral influences on weight
gain during pregnancy

• Hicky, CA. Am J Clin Nutr. 200071(supple)1364S
  -70S.

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Percent of Women Gaining lt 7.3 kg
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Characteristics of Women Associated with
Inadequate Weight Gain

• Lower education levels
• Unmarried
• Aged gt 30 years
• Smoking
• Multiple parity

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• Possibly psycho-social stress and pregnancy
  intendedness (effects seem to differ by culture)
• Low income women had twice the risk in NNS.
• Migrant workers have higher risk in WIC
  populations

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1997 Review of Recommendations

• Maternal Weight Gain A Report of an Expert Work
  Group. Suitor, CW. 1997. NCEMCH.

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Recent Findings

• Maternal water gain, which probably represents
  lean tissue, is a predictor of birthweight, fat
  gain is not predictive.
• Effect size of energy intake on weight gain is
  modest.
• When maternal weight gain is within IOM range,
  incidence of SGA LBW is reduced

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Recent Findings, cont.

• Increasing prevalence of obesity in population
  calls for reexamination of effects of pregnancy
  weight gain retention
• Increased parity is associated with increased
  weight gain in adulthood.
• Post delivery, African American women have
  greater weight retention than white women with
  the same pregnancy weight gain.

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Recommendations for Practice

• Promote use of IOM recommendations for rate of
  weight gain as well as total weight gain.
• Promote strategies for weight gain within
  recommended ranges.
• Promote healthy eating

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• Until more is known, two groups of special
  concern, Adolescents and African American women
  should be advised to stay within IOM ranges
  without either restricting weight gain or
  encouraging weight gain at the upper end of the
  range.

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Multiple Births

• Optimal range of birthweight
• Twins 2500-2800 g at 36-37 weeks
• Triplets 1900-2000 g at 34-36 weeks
• Maternal weight gain of 40-50 pounds with 1.5
  pounds per week during second half of pregnancy
  is associated with optimal twin birthweights
• Weight gain of lt 0.85 pounds per week before 24
  weeks associated with IUGR and morbidity.

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Carmichael- what are women actually doing? (AJPH,
1998)

• Cohort 7002 singleton deliveries with good
  outcomes at UCSF between 1980-1990
• Good outcomes vaginal delivery, term (gt37
  weeks), live, AGA, no maternal diabetes or
  hypertension

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Carmichael Results
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Carmichael Discussion

• More than half the women fell outside of IOM
  ranges
• Higher gains may be associated with higher
  postpartum weight retention
• Monitoring of weight gain is not highly sensitive
  when used in isolation
• Many questions remain about the utility of
  monitoring weight gain, standards, and counseling.