The average gestational period for humans is 40 weeks. This is divided into three trimesters.

Antenatal care

In obstetric practice, an obstetrician or midwife will see a pregnant woman on a regular basis to check the progress of the pregnancy. An individual woman’s schedule of antenatal appointment varies depending on local resources and her risk factors, such as diabetes.

The main rationale for these visits is surveillance for diseases of pregnancy which are detectable. Some examples are:

1. pre-eclampsia. The blood-pressure and urine of a pregnant woman is checked at every opportunity to check for this.
2. placenta praevia. On ultrasound, the placenta is visible obstructing the birth canal
3. abnormal presentation (late pregnancy only). The fetus may be feet-first or buttocks-first(breech), side-on (transverse), or at an angle (oblique presentation)
4. IUGR (Intrauterine Growth Restriction), this is a general designation, where the fetus is too small for its gestational age. Causes can be intrinsic (in the fetus) or extrinsic (usually placental problems). IUGR refers to fetal growth that is less than 10% of what is expected at that gestational age.

Trimesters

First trimester: elevated ?-hCG (human chorionic gonadotrophin)of up to 100,000 mIU/mL by 10 weeks GA can cause morning sickness, fatigue, mood swings and food cravings. The symptoms can last through 12 to 16 weeks of gestation.

Second trimester: The abdomen shows an obvious swelling arising from the pelvis, starting the “obvious phase” of pregnancy. Hyperpigmentation, including linea nigra, may appear.

Third trimester: The mother may experience backaches due to increased strain. Typically, the curvature of the spine is changed as pregnancy evolves in order to counteract the change in weight distribution. The mother may also suffer mild urinary incontinence due to pressure on the bladder by the pregnant uterus, as well as heartburn (due to compression of the stomach).

Overall

* Bluish discoloration of vagina and cervix (Chadwick’s sign)
* Softening and cyanosis of cervix after 4 weeks (Goodell’s sign)
* Softening of uterus after 6 weeks (Ladin’s sign)
* Breast swelling and tenderness
* Linea nigra from umbilicus to pubis
* Telangiectasias
* Palmar erythema
* Amenorrhea
* Nausea and vomiting
* Breast pain
* Fetal movement
* Sciatica (Pain caused by compression of the sciatic nerve)

Maternal physiology

During pregnancy, the woman undergoes many physiological changes, which are entirely normal, including cardiovascular, hematologic, metabolic, renal and respiratory changes that become very important in the event of complications.

Cardiovascular

The woman is the sole provider of nourishment for the embryo and later, the fetus, and so her plasma and blood volume slowly increase by 40-50% over the course of the pregnancy to accommodate the changes. This results in overall vasodilation, an increase in heart rate (15 beats/min more than usual), stroke volume, and cardiac output. Cardiac output increases by about 50%, mostly during the first trimester. The systemic vascular resistance also drops due to the smooth muscle relaxation caused by elevated progesterone, leading to a fall in blood pressure. Diastolic blood pressure consequently decreases between 12-26 weeks, and increases again to prepregnancy levels by 36 weeks. If the blood pressure remains abnormal beyond 36 weeks, the woman should be investigated for pre-eclampsia, a condition that precedes eclampsia.

Hematology

* The plasma volume increases by 50% and the red blood cell volume increases only by 20-30%.
* Consequently, the hematocrit decreases.
* White blood cell count increases and may peak at over 20 mil/mL in stressful conditions.
* Decrease in platelet concentration to a minimal normal values of 100-150 mil/mL
* The pregnant woman also becomes hypercoagulable due to increased liver production of coagulation factors, mainly fibrinogen and factor VIII.

Metabolism

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 hemoglobin.

Nutrition

* Increased caloric requirement by 300 kcal/day
* Gain of 20 to 30 lb (10 to 15 kg)
* Increased protein requirement to 70 or 75 g/day
* Increased folate requirement from 0.4 to 0.8 mg/day (important in preventing neural tube defects)

All patients are advised to take prenatal vitamins to compensate for the increased nutritional requirements. The use of Omega 3 fatty acids supports mental and visual development of infants source Choline supplementation of research mammals supports mental development that lasts throughout life source

Gastrointestinal

* nausea and vomiting (“morning sickness”) due to elevated B-hCG, which should resolve by 14 to 16 weeks
* prolonged gastric empty time
* decreased gastroesophageal sphincter tone, which can lead to acid reflux
* decreased colonic motility, which leads to increased water absorption and constipation

Renal

* Increase in kidney and ureter size
* Increased glomerular filtration rate (GFR) by 50%, which subsides around 20 weeks postpartum
o Decreased BUN (blood urea nitrogen) and creatinine, and glucosuria (due to saturated tubular reabsorption)
+ Persistent glucosuria can suggest gestational diabetes
* Increased renin-angiotensin system, causing increased aldosterone levels
o Plasma sodium does not change because this is offset by the increase in GFR

Pulmonary

* Increased tidal volume (30-40%)
* Decreased total lung capacity (TLC) by 5% due to elevation of diaphragm from uteral compression
* Decreased expiratory reserve volume
* Increased minute ventilation (30-40%) which causes a decrease in PaCO2 and a compensated respiratory alkalosis

All of these changes can contribute to the dyspnea (shortness of breath) that a pregnant woman may experience.

Endocrine

* Increased estrogen, which is mainly produced in the placenta
o Fetal well being is associated with maternal estrogen levels
o Causes an increase in thyroxine-binding globulin (TBG)
* Increased human chorionic gonadotropin (?-hCG), which is produced by the placenta. This maintains progesterone production by the corpus luteum
* Human placental lactogen (hPL) is produced by the placenta and ensures nutrient supply to the fetus. It also causes lipolysis and is an insulin antagonist, which is a diabetogenic effect.
* Increased progesterone production, first by corpus luteum and later by the placenta. Its main course of action is to relax smooth muscle.
* Increased prolactin
* Increased alkaline phosphatase

Musculoskeleton and dermatology

* Lower back pain due to a shift in gravity
* Increased estrogen can cause spider angiomata and palmar erythema
* Increase melanocyte-stimulating hormone (MSH) can cause hyperpigmentation of nipples, umbilicus, abdominal midline (linea nigra), perineum, and face (melasma or chloasma)

Others

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

Prenatal care

Main article: Prenatal care

Prenatal care is important in screening for various complications of pregnancy. This includes routine office visits with physical exams and routine lab tests:

First trimester

* complete blood count (CBC)
* blood type (blood transfusion may be needed in an emergency)
* general antibody screen (indirect Coombs test) for HDN
o Rh D negative antenatal patients should receive RhoGam at 28 weeks to prevent Rh disease.
* Rapid plasma reagent (RPR) which screens for syphilis
* Rubella antibody screen
* Hepatitis B surface antigen
* Gonorrhea and Chlamydia culture
* PPD for tuberculosis
* Pap smear
* Urinalysis and culture
* HIV screen
* Group B Streptococcus screen — will receive IV penicillin if positive (if mother is allergic, alternate therapies include IV clindamycin or IV vancomycin)

Second trimester

* MSAFP/triple screen (maternal serum alpha-fetoprotein) – elevation correlated with neural tube defects and decrease correlated with Down’s syndrome
* ultrasound
* amniocentesis in older patients

Third trimester

* hematocrit (if low, mother will receive iron supplementation)
* glucose loading test (GLT) – screens for gestational diabetes; if > 140 mg/dL, a glucose tolerance test (GTT) is administered; if fasting glucose > 105 mg/dL, gestational diabetes is suggestive.

Complications

See Complications of Pregnancy

Fetal assessments

Common

* ultrasound is used for many functions:
o Dating the gestational age of a pregnancy, most accurate in first trimester
o Detecting fetal anomalies in the second trimester
o biophysical profiles (BPP)
o Blood flow velocity in umbilical cord — decrease/absence/reversal or diastolic blood flow in the umbilical artery is worrisome.
o Congenital anomalies can be diagnosed with second trimester ultrasound
* Fetal karyotype for the screening of genetic diseases can be obtained via amniocentesis or chorionic villus sampling (CVS)

Uncommon

* Fetal hematocrit for the assessment of fetal anemia, Rh isoimmunization, or hydrops can be determined by percutaneous umbilical blood sampling (PUBS) which is done by placing a needle through the abdomen into the uterus and taking a portion of the umbilical cord.
* Fetal lung maturity is associated with how much surfactant the fetus is producing. Reduced production of surfactant indicates decreased lung maturity and is a high risk factor for neonatal respiratory distress syndrome (NRDS). Typically a lecithin:sphingomyelin ratio greater than 1.5 is associated with increased lung maturity.
* Nonstress test (NST) for fetal heart rate
* Oxytocin challenge test

Induction

Reasons to induce include:

1. pre-eclampsia
2. IUGR
3. diabetes
4. other general medical condition, such as renal disease

Induction may occur any time after 24 weeks of gestation if the risk to the fetus or mother is greater than the risk of delivering a premature fetus regardless of lung maturity. Prior to 32 weeks gestation steroids are given to the mother to help mature the fetus’s lungs.

If a woman does not eventually labour by 41-42 weeks, induction may be performed, as the placenta may become unstable after this date.

Induction may be achieved via several methods:

1. pessary of Prostin cream, prostaglandin E2
2. vaginal or oral administration of misoprostol
3. cervical insertion of a 30-mL Foley catheter
4. surgical induction, by piercing the amnion
5. infusion of oxytocin

Labour

During labour itself, the obstetrician may be called on to do a number of things:

1. monitor the progress of labour, by reviewing the nursing chart, performing vaginal examination, and assessing the trace produced by a foetal monitoring device (the cardiotocograph)
2. accelerate the progress of labour by infusion of the hormone oxytocin
3. provide pain relief, either by nitrous oxide (nowadays uncommon, at least in the U.S.), opiates, or by epidural anesthesia done by anaethestists or an anesthesiologist
4. surgically assisting labour, by forceps or the Ventouse (a suction cap applied to the fetus’ head)
5. Caesarean section, if vaginal delivery is decided against or appears too difficult. Caesarean section can either be elective, that is, arranged before labour, or decided during labour as an alternative to hours of waiting. True “emergency” Cesarean sections (where minutes count) are a rarity.

Antenatal

During the time immediately after birth both baby as well as mother are hormonally cued to bond, the mother through the release of oxytocin a hormone also released with breastfeeding.

Emergencies in obstetrics

Two main emergencies are ectopic pregnancy and (pre)eclampsia.

* Ectopic pregnancy is when an embryo implants in the Fallopian tube or (rarely) on the ovary or inside the peritoneal cavity. This may cause massive internal bleeding.
* Pre-eclampsia is a disease caused by mysterious toxins secreted by the placenta. These toxins act on the vascular endothelium, causing hypertension and proteinuria. If severe, it progresses to fulminant pre-eclampsia, with headaches and visual disturbances. This is a prelude to eclampsia, where a convulsion occurs, which is often fatal.

Imaging, monitoring and care

In present society, medical science has developed a number of procedures to monitor pregnancy.

Antenatal record

On the first visit to her obstetrician or midwife, the pregnant woman is asked to carry out the antenatal record, which constitutes a medical history and physical examination.

On subsequent visits, the gestational age (GA) is rechecked with each visit. Symphysis-fundal height (dsddsdsddSFH; in cm) should equal gestational age after 20 weeks of gestation, and the fetal growth should be plotted on a curve during the antenatal visits. The fetus is palpated by the midwife or obstetrician using Leopold maneuver to determine the position of the baby. Blood pressure should also be monitored, and may be up to 140/90 in normal pregnancies. High blood pressure indicates hypertension and possibly pre-eclampsia, if severe swelling (edema) and spilled protein in the urine are also present.

Fetal screening is also used to help assess the viability of the fetus, as well as congenital problems. Genetic counseling is often offered for families who may be at an increased risk to have a child with a genetic condition. Amniocentesis at around the 20th week is sometimes done for women 35 or older to check for Down’s Syndrome and other chromosome abnormalities in the fetus. Even earlier than amniocentesis is performed, the mother may undergo the triple test, nuchal screening, nasal bone, alpha-fetoprotein screening and Chorionic villus sampling, also to check for disorders such as Down Syndrome. Amniocentesis is a prenatal genetic screening of the fetus, which involves inserting a needle through the mother’s abdominal wall and uterine wall, to extract fetal DNA from the amniotic fluid. There is a risk of miscarriage and fetal injury with amniocentesis since it involves penetrating the uterus with the baby still in utero.

Imaging is another important way to monitor a pregnancy. The mother and fetus are also usually imaged in the first trimester of pregnancy. This is done to predict problems with the mother; confirm that a pregnancy is present inside the uterus; guess the gestational age; determine the number of fetuses and placentae; evaluate for an ectopic pregnancy and first trimester bleeding; and assess for early signs of anomalies.

X-rays and computerized bimarestan shahd beheshti tomography (CT) are not used, especially in the first trimester, due to the ionizing radiation, which has teratogenic effects on the fetus. Instead, ultrasound is the imaging method of choice in the first trimester and throughout the pregnancy, since it emits no radiation, is portable, and allows for realtime imaging. Ultrasound imaging may be done at any time throughout the pregnancy, but usually happens at the 12th week (dating scan) and the 20th week (detailed scan).

A normal gestation would reveal a gestational sac, yolk sac, and fetal pole. The gestational age can be assessed by evaluating the mean gestation sac diameter (MGD) before week 6, and the crown-rump length after week 6. Multiple gestation is evaluated by the number of placentae and amniotic sacs present.

Pregnancy has different cultural aspects related to the perception of the body, the relationship with partner and to the meaning of the event.

Terms and definitions

* embryo – conceptus between time of fertilization to 10 weeks of gestation
* fetus – from 10 weeks of gestation to time of birth
* infant – time of birth to 1 year of age
* gestational age – time from last menstrual period (LMP) up to present
* first trimester – up to 14 weeks of gestation
* second trimester – 14 to 28 weeks of gestation
* third trimester – 28 weeks to delivery
* viability – minimum age for fetus survival, ca. third trimester
* previable infant – delivered prior to 24 weeks
* preterm infant – delivered between 24-37 weeks
* term infant – delivered between 37-42 weeks
* gravidity (G) – number of times a woman has been pregnant
* parity (P) – number of pregnancies with a birth beyond 20 weeks GA or an infant weighing more than 500 g
* Ga Pw-x-y-z – a = number of pregnancies, w = number of term births, x = number of preterm births, y = number of miscarriages, z = number of living children; for example, G4P1-2-1-3 means the woman had a total of 4 pregnancies, of which 1 is of term, 2 are preterm, 1 miscarriage, and 3 total living children (1 term + 2 preterm).

In the last few years, medical malpractice suits and skyrocketing insurance premiums have forced many American obstetricians and gynaecologists to leave or limit their practice. Medical students are increasingly choosing not to specialize in obstetrics (see Bower 2003). This all adds up to fewer obstetricians in some states and fewer health care options for women, though it has led to higher average salaries, as an article by Medical Economics points out.