Pregnancy

A pregnant woman near the end of her term
Pregnancy
Classification and external resources
ICD-9 V22

Pregnancy (latin graviditas) is the carrying of one or more offspring, known as a fetus or embryo, inside the uterus of a female. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets. Human pregnancy is the most studied of all mammalian pregnancies. Obstetrics is the surgical field that studies and cares for high risk pregnancy. Midwifery is the non-surgical field that cares for pregnancy and pregnant women.

Childbirth usually occurs about 38 weeks after fertilization (conception), i.e., approximately 40 weeks from the last normal menstrual period (LNMP) in humans. The date of delivery is considered normal medically if it falls within two weeks of the calculated date. The calculation of this date involves the assumption of a regular 28-day period. Thus, pregnancy lasts almost nine months.

The exact definition of the English word “pregnancy” is a subject of political controversy, but it is not a matter of substantial controversy in the medical community.

Terminology

One scientific term for the state of pregnancy is gravid, and a pregnant female is sometimes referred to as a gravida.[1] Neither word is used in common speech. Similarly, the term "parity" (abbreviated as "para") is used for the number of previous successful live births. Medically, a woman who has never been pregnant is referred to as a "nulligravida", and in subsequent pregnancies as "multigravida" or "multiparous".[2][3][4] Hence during a second pregnancy a woman would be described as "gravida 2, para 1" and upon delivery as "gravida 2, para 2". Incomplete pregnancies of abortions, miscarriages or stillbirths account for parity values being less than the gravida number, whereas a multiple birth will increase the parity value. Women who have never carried a pregnancy achieving more than 20 weeks of gestation age are referred to as "nulliparous".[5]

The term embryo is used to describe the developing offspring during the first eight weeks following conception, and the term fetus is used from about two months of development until birth.[6][7]

In many societies' medical or legal definitions, human pregnancy is somewhat arbitrarily divided into three trimester periods, as a means to simplify reference to the different stages of prenatal development. The first trimester carries the highest risk of miscarriage (natural death of embryo or fetus). During the second trimester, the development of the fetus can be more easily monitored and diagnosed. The beginning of the third trimester often approximates the point of viability, or the ability of the fetus to survive, with or without medical help, outside of the uterus.[8]

Physiological changes in pregnancy

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.

Hormonal changes

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 also decreases maternal tissue sensitivity to insulin, resulting in gestational diabetes.

Musculoskeletal changes

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 symphysis pubis and sacroiliac widen or have increased laxity.

Physical changes

Weight is gained during pregnancy due to increased appetite, fat deposition, and growth of the reproductive organs and fetus, as well as increased blood volume and water retention. Anywhere from 5 pounds (2.3 kg) to over 100 pounds (45 kg) can be gained during pregnancy. In America, the doctor-recommended weight gain range 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.

Other physical changes during pregnancy include breasts increasing two cup sizes. Also areas of the body such as the forehead and cheeks (known as the 'mask of pregnancy') become darker due to the increase of melanin being produced.[24]

The female body experiences many changes as the fetus grows through each trimester as shown and discussed in this pregnancy video. Two women at different stages in their pregnancy illustrate what has happened to their bodies.

Cardiovascular changes

Blood volume increases by 40% in the first two trimesters. This is due to an increase in plasma volume through increased aldosterone. Progesterone may also interact with the aldosterone receptor, thus leading to increased levels. Red blood cell numbers increase due to increased erythropoietin levels.

Cardiac function is also modified, with increase heart rate and increased stroke volume. A decrease in vagal tone and increase in sympathetic tone is the cause. Blood volume increases act to increase stroke volume of the heart via Starling's law. After pregnancy the change in stroke volume is not reversed. Cardiac output rises from 4 to 7 litres in the 2nd trimester

Blood pressure also fluctuates. In the first trimester it falls. Initially this is due to decreased sensitivity to angiotensin and vasodilation provoked by increased blood volume. Later, however, it is caused by decreased resistance to the growing uteroplacental bed.

Respiratory changes

Decreased functional residual capacity is seen, typically falling from 1.7 to 1.35 litres, due to the compression of the diaphragm by the uterus. Tidal volume increases, from 0.45 to 0.65 litres, giving an increase in pulmonary ventilation. This is necessary to meet the increased oxygen requirement of the body, which reaches 50ml/min - 20ml of which goes to reproductive tissues.

Progesterone may act centrally on chemoreceptors to reset the set point to a lower partial pressure of carbon dioxide. This maintains an increased respiration rate even at a decreased level of carbon dioxide.

Metabolic changes

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. Increase liver metabolism is also seen, with increased gluconeogenesis to increase maternal glucose levels.

Renal changes

Renal plasma flow increases, as does aldosterone and erthropoietin production as discussed. The tubular maximum for glucose is reduced, which may precipitate gestational diabetes.

Management

Prenatal medical care is of recognized value throughout the developed world. Periconceptional Folic acid supplementation is the only type of supplementation of proven efficacy.

Drugs in pregnancy

Main article: Drugs in pregnancy

Drugs used during pregnancy can have temporary or permanent effects on the fetus. Therefore many physicians would prefer not to prescribe for pregnant women, the major concern being over teratogenicity of the drugs. This results in inappropriate treatment of pregnant women. Use of drugs in pregnancy is not always wrong. For example, high fever is harmful for the fetus in the early months. Use of paracetamol is better than no treatment at all. Also, diabetes mellitus during pregnancy may need intensive therapy with insulin. Drugs have been classified into categories A,B,C,D and X based on the Food and Drug Administration(FDA) rating system to provide therapeutic guidance based on potential benefits and fetal risks. Drugs like multivitamins that have demonstrated no fetal risks after controlled studies in humans are classified as Category A. On the other hand drugs like thalidomide with proven fetal risks that outweigh all benefits are classified as Category X.[56]

Sexuality during pregnancy

Most pregnant women can enjoy sexual intercourse throughout gravidity. Most research suggests that, during pregnancy, both sexual desire and frequency of sexual relations decrease.[57][58] In context of this overall decrease in desire, some studies indicate a second-trimester increase, preceding a decrease.[59] However, these decreases are not universal: a significant number of women report greater sexual satisfaction throughout their pregnancies.[60]

Sex during pregnancy is a low-risk behaviour except when the physician advises that sexual intercourse be avoided, which may, in some pregnancies, lead to serious pregnancy complications or health issues such as a high-risk for premature labour or a ruptured uterus. Such a decision may be based upon a history of difficulties in a previous childbirth.

Some psychological research studies in the 1980s and '90s contend that it is useful for pregnant women to continue to have sexual activity, specifically noting that overall sexual satisfaction was correlated with feeling happy about being pregnant, feeling more attractive in late pregnancy than before pregnancy and experiencing orgasm.[59] Sexual activity has also been suggested as a way to prepare for induced labour; some believe the natural prostaglandin content of seminal liquid can favour the maturation process of the cervix making it more flexible, allowing for easier and faster dilation and effacement of the cervix. However, the efficacy of using sexual intercourse as an induction agent "remains uncertain".[61]

During pregnancy, the fetus is protected from penetrative thrusting by the amniotic fluid in the womb and by the woman's abdomen.[62]

After giving birth sexual intercourse can begin when the couple are both ready. However most couples wait until after six weeks and they should consult their GP if they have any concerns.[24]

Abortion

Main article: Abortion

An abortion is the removal or expulsion of an embryo or fetus from the uterus, resulting in or caused by its death. This can occur spontaneously or accidentally as with a miscarriage, or be artificially induced by medical, surgical or other means.

Progression

Complaints

See also: Complications of pregnancy

The following are complaints that may occur during pregnancy:

  • Back pain. A particularly common complaint in the third trimester when the patient's center of gravity has shifted.
  • Constipation. A complaint that is caused by decreased bowel motility secondary to elevated progesterone (normal in pregnancy), which can lead to greater absorption of water.
  • Braxton Hicks contractions. Occasional, irregular, and often painless contractions that occur several times per day.
  • Edema (swelling). Common complaint in advancing pregnancy. Caused by compression of the inferior vena cava (IVC) and pelvic veins by the uterus leads to increased hydrostatic pressure in lower extremities.
  • Regurgitation, heartburn, and nausea. Common complaints that may be caused by Gastroesophageal Reflux Disease (GERD); this is determined by relaxation of the lower esophageal sphincter (LES) and increased transit time in the stomach (normal in pregnancy)
  • Haemorrhoids. Complaint that is often noted in advancing pregnancy. Caused by increased venous stasis and IVC compression leading to congestion in venous system, along with increased abdominal pressure secondary to the pregnant space-occupying uterus and constipation.
  • Pelvic girdle pain. A common complaint is pain, instability or dysfunction of the symphysis pubis and/or sacroiliac joints resulting from either excess strain or injury (such as Diastasis symphysis pubis) during the course of the pregnancy or birthing process.
  • Increased urinary frequency. A common complaint referred by the gravida, caused by increased intravascular volume, elevated GFR (glomerular filtration rate), and compression of the bladder by the expanding uterus.
  • Varicose veins. Common complaint caused by relaxation of the venous smooth muscle and increased intravascular pressure.

Childbirth

Main article: Childbirth

Childbirth is the process whereby an infant is born. It is considered by many to be the beginning of a person's life, and age is defined relative to this event in most cultures.

A woman is considered to be in labour when she begins experiencing regular uterine contractions, accompanied by changes of her cervix — primarily effacement and dilation. While childbirth is widely experienced as painful, some women do report painless labours, while others find that concentrating on the birth helps to quicken labour and lessen the sensations. Most births are successful vaginal births, but sometimes complications arise and a woman may undergo a caesarean section.

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

Postnatal period

Main article: Postnatal

Context

There are fine distinctions between the concepts of fertilization and the actual state of pregnancy, which starts with implantation. In a normal pregnancy, the fertilization of the egg usually will have occurred in the Fallopian tubes or in the uterus. (Often, an egg may become fertilized yet fail to become implanted in the uterus.) If the pregnancy is the result of in-vitro fertilization, the fertilization will have occurred in a Petri dish, after which pregnancy begins when one or more zygotes implant after being transferred by a physician into the woman's uterus.

In the context of political debates regarding a proper definition of life, the terminology of pregnancy can be confusing. The medically and politically neutral term which remains is simply "pregnancy," though this can be problematic as it only refers indirectly to the embryo or fetus. De Crespigny observes that doctors' language has a powerful influence over the way patients think, and thus proposes that the best interests of patients are served by using language that both supports patient autonomy and is neutral.[63]

See also

References

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