Obstetrics (from the
Latin obstare, "to stand by") is the
surgical specialty dealing with the care of women and their children during
pregnancy,
childbirth and
postnatal.
Midwifery is the non-medical equivalent.
Veterinary obstetrics is the same concept for
veterinary medicine.
Antenatal care
In obstetric practice, an obstetrician or midwife sees a pregnant woman on a regular basis to check the progress of the pregnancy, to verify the absence of ex-novo disease, to monitor the state of preexisting disease and its possible effect on the ongoing pregnancy. A woman's schedule of antenatal appointment varies according to the presence of risk factors, such as
diabetes, and local resources.
Some of the clinically and statistically more important risk factors that must be systematically excluded, especially in advancing pregnancy, are
pre-eclampsia, abnormal placentation, abnormal fetal presentation and
intrauterine growth restriction. For example, to identify
pre-eclampsia, blood-pressure and albuminuria (level of
urine protein) are checked at every opportunity.
Placenta praevia must be excluded (PP = low lying placenta that, at least partially, obstructs the birth canal and therefore warrants elective caesarean delivery); this can only be achieved with the use of an
ultrasound scan. However, early placenta praevia is not alarming; this is because as the uterus grows along the pregnancy, the placenta may still move away. A placenta praevia is of clinical significance as from the 28th week of gestation. The current management includes a caesarean section. The type of caesarean section is determined by the position (anterior or posterior) of the placenta.
In late pregnancy fetal presentation must be established: cephalic presentation (head first) is the norm but the fetus may present feet-first or buttocks-first (
breech), side-on (transverse), or at an angle (oblique presentation).
Intrauterine growth restriction is a general designation where the fetus is smaller than expected when compared to its gestational age (in this case, fetal growth parameters show a tendency to drop off from the 50th percentile eventually falling below the 10th percentile, when plotted on a fetal growth chart). Causes can be intrinsic (to the fetus) or extrinsic (maternal or placental problems).
Maternal Change
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 pre-pregnancy levels by 36 weeks. If the blood pressure becomes abnormally high, the woman should be investigated for
pre-eclampsia and other causes of
hypertension.
Endocrine
Pregnant women experience adjustments in their
endocrine system. These adjustments include an increase in her
estrogen levels; which is mainly produced by the
placenta and is associated with fetal well–being. Women also experience increased
human chorionic gonadotropin (β-hCG); which is produced by the placenta. This maintains
progesterone production by the
corpus luteum. Additionally,
human placental lactogen (hPL) is produced by the placenta, ensuring nutrient supply to the fetus. This also causes
lipolysis and is an
insulin antagonist, which is a diabetogenic effect.
Additionally, there is increased
prolactin, increased
alkaline phosphatase, and increased progesterone production, first by corpus luteum and later by the placenta, whose main course of action is to relax smooth muscle.
Gastrointestinal
During pregnancy, woman can experience nausea and vomiting (
morning sickness); which may be due to elevated
B-hCG and should resolve by 14 to 16 weeks. Additionally, there is prolonged gastric empty time, decreased gastroesophageal sphincter tone, which can lead to
acid reflux, and decreased colonic motility, which leads to increased water absorption and
constipation.
Hematology
During pregnancy the
plasma volume increases by 50% and the red blood cell volume increases only by 20-30%.
Consequently, the
hematocrit decreases on lab value, however this is not a true decrease in hematocrit, but rather due to the dilution. The white blood cell count increases and may peak at over 20 mg/mL in stressful conditions. Conversely, there is a decrease in platelet concentration to a minimal normal values of 100-150 mil/mL.
A pregnant woman will also become
hypercoagulable, leading to increased risk for developing blood clots and embolisms, due to increased
liver production of coagulation factors, mainly
fibrinogen and
factor VIII (this hypercoagulable state along with the decreased ambulation causes an increased risk of both DVT and PE). Women are at highest risk for developing clots, or thrombi, during the weeks following labor. Clots usually develop in the left leg or the left iliac venous system. The left side is most afflicted because the left iliac vein is crossed by the right iliac artery. The increased flow in the right iliac artery after birth compresses the left iliac vein leading to an increased risk for thrombosis (clotting) which is exacerbated by the aforementioned lack of ambulation following delivery. Both underlying
thrombophilia and
cesarean section can further increase these risks.
Edema, or swelling, of the feet is common during pregnancy, partly because the enlarging uterus compresses veins and lymphatic drainage from the legs.
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.
Neurophysiologic
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. The body must change its physiological and homeostatic mechanisms in pregnancy to ensure the fetus is provided for. Increases in blood sugar, breathing and cardiac output are all required. Levels of progesterone and oestrogens rise continually throughout pregnancy, suppressing the hypothalamic axis and subsequently the menstrual cycle. The woman and the placenta also produce many hormones.
Prolactin levels increase due to maternal Pituitary gland enlargement by 50%. This mediates a change in the structure of the Mammary gland from ductal to lobular-alveolar. Parathyroid hormone is increased due to increases of calcium uptake in the gut and reabsorption by the kidney. Adrenal hormones such as cortisol and aldosterone also increase.
Placental lactogen is produced by the placenta and stimulates lipolysis and fatty acid metabolism by the woman, conserving blood glucose for use by the fetus. It can also decrease maternal tissue sensitivity to insulin, resulting in gestational diabetes
Nutrition
Nutritionally, pregnant women require a caloric increase caloric of 300 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 is experienced.
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.
Choline supplementation of research mammals supports mental development that lasts throughout life.
Renal
A pregnant woman may experience an increase in kidney and ureter size. There is also an increase in the
glomerular filtration rate (GFR) by 50%, which subsides around 20 weeks
postpartum.
Plasma
sodium does not change because this is offset by the increase in GFR. Additionally, there is decreased
blood urea nitrogen (BUN) and
creatinine, and glucosuria (due to saturated tubular reabsorption), persistent glucosuria may suggest
gestational diabetes, and increased
renin-angiotensin system, causing increased
aldosterone levels.
Pulmonary
Changes in pulmonary activity for pregnant woman can include increased
tidal volume (30-40%), decreased
total lung capacity (TLC) by 5% due to elevation of diaphragm from uteral compression, decreased
expiratory reserve volume, and increased
minute ventilation (30-40%) which causes a decrease in PaCO2 and a compensated
respiratory alkalosisAll of these changes can contribute to the
dyspnea (shortness of breath) that a pregnant woman may experience.
Other
Other conditions that can be encountered include:
- Lower back pain due to a shift in gravity
- Increase melanocyte-stimulating hormone (MSH) can cause hyperpigmentation of nipples, umbilicus, abdominal midline (linea nigra), perineum, and face (melasma or chloasma)
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
- * Rh D negative antenatal patients should receive RhoGam at 28 weeks to prevent Rh disease.
- Group B Streptococcus screen – will receive IV penicillin or ampicillin (it is much cheaper and has a wider coverage)if positive (if mother is allergic, alternative therapies include IV clindamycin or IV vancomycin)
genetic screening for downs syndrome (trisomy 21) and trisomy 18
the national standard in the United States is rapidly evolving away from the AFP-Quad screen for downs syndrome- done typically in the second trimester at 16–18 weeks. The newer integrated screen (formerly called F.A.S.T.E.R for First And Second Trimester Early Results) can be done at 10 plus weeks to 13 plus weeks with an ultrasound of the fetal neck (thick skin is bad) and two chemicals (analytes) Papp-a and bhcg (pregnancy hormone level itself). It gives an accurate risk profile very early. There is then a second blood screen at 15 to 20 weeks which refines the risk more. The cost is higher than an afp-quad screen due to the ultrasound and second blood test but it is quoted to have a 92% pick up rate.
Second trimester
- Ultrasound either abdominal or trannsvaginal to assess cervix, placenta, fluid and baby
- Amniocentesis is the national standard for women over 35 or who reach 35 by mid pregnancy or who are at increased risk by family history or prior birth history
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; a fasting glucose > 105 mg/dL suggests gestational diabetes.
Most doctors do a sugar load in a drink form of 50 grams of glucose in cola, lime or orange and draw blood an hour later (plus or minus 5 minutes) ; the standard modified criteria have been lowered to 135 since the late 1980s
Complications
Fetal assessments
Ultrasound is routinely used for dating the gestational age of a pregnancy from the size of the foetus, the most accurate dating being in first trimester before the growth of the fetus has been significantly influenced by other factors. Ultrasound is also used for detecting congenital anomalies (or other fetal anomalies) and determining the
biophysical profiles (BPP), which are generally easier to detect in the second trimester when the fetal structures are larger and more developed. Specialised ultrasound equipment can also evaluate the blood flow velocity in the
umbilical cord, looking to detect a decrease/absence/reversal or diastolic blood flow in the umbilical artery.
Other tools used for assessment include:
Childbirth
Induction
Induction is a method of artificially or prematurely stimulating labour in a woman. Reasons to induce can include
pre-eclampsia, the
birth mass, diabetes, and other various general medical conditions, such as
renal disease. Induction may occur any time after 34 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. 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:
- Rupturing the amniotic membranes
- Intravenous infusion of synthetic oxytocin (Pitocin or Syntocinon)
Labor
During labor itself, the obstetrician/doctor/intern/medical student under supervision may be called on to do a number of tasks. These tasks can include:
- Monitor the progress of labor, by reviewing the nursing chart, performing vaginal examination, and assessing the trace produced by a fetal monitoring device (the cardiotocograph)
- Accelerate the progress of labor by infusion of the hormone oxytocin
- Surgically assisting labor, by forceps or the Ventouse (a suction cap applied to the fetus' head)
- Caesarean section, if there is an associated risk with vaginal delivery, as such fetal or maternal compromise supported by evidence and literature. Caesarean section can either be elective, that is, arranged before labor, or decided during labor as an alternative to hours of waiting. True "emergency" Cesarean sections include abruptio placenta, and are more common in multigravid patients, or patients attempting a Vaginal Birth After Caeserean section (VBAC).
Emergencies in obstetrics
The main emergencies include:
- 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 which is defined by a combination of signs and symptoms that are related to maternal hypertension. The cause is unknown, and markers are being sought to predict its development from the earlist stages of pregnancy. Some unknown factors cause vascular damage in the endothelium, causing hypertension. If severe, it progresses to eclampsia, where a convulsions occur, which can be fatal. Preeclamptic patients with the HELLP syndrome show liver failure and Disseminated intravascular coagulation (DIC).
- Shoulder dystocia where one of the fetus' shoulders becomes stuck during vaginal birth, especially in macrosomic babies of diabetic mothers.
- Uterine rupture can occur during obstructed labor and endangered fetal and maternal life.
- Prolapsed cord refers to the prolapse of the fetal cord during labor with the risk of fetal suffocation.
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 (SFH; 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 because it involves penetrating the uterus with the baby still in utero.
Imaging
A dating
scan at 12 weeks.
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; estimate 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 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, because 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 gestational 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.
Salary
The salary of an obstetrician varies from country to country:
See also
