What is Pregnancy?

What is Pregnancy?

Detection and dating

Timeline of a typical pregnancy

Medical aspects of pregnancy

Birth

Postnatal Period

What is Pregnancy?

Pregnancy is the carrying of one or more embryos or foeti by female mammals, including humans, inside their bodies. In a pregnancy there can be multiple gestations (for example, in the case of twins, or triplets). Human pregnancy is the most studied of all mammalian pregnancies.

Human pregnancy lasts approximately 40 weeks between the time of the last menstrual cycle and birth (38 weeks from fertilisation). The medical term for a pregnant woman is "gravida," just as the medical term for the unborn human is an embryo (early weeks) and then "fetus" (until birth). A woman who is pregnant for the first time is known as a primigravida or gravida 1: a woman who has never been pregnant is known as a gravida 0; similarly, the terms para 0 and para 1 are used for the number of times a woman has given birth.

In many societies' medical and legal definitions, human pregnancy is arbitrarily divided into three trimester periods, as a means to simplify reference to the different stages of fetal development. The first trimester period carries the highest risk of miscarriage (natural death of embryo or fetus), while during the second trimester the development of the fetus can start to be monitored and diagnosed. The third trimester marks the beginning of viability, which means the fetus can survive if an early natural or induced birth occurs. Because of the possible viability of developed fetus, cultural and legal definitions of life often consider a fetus in the third trimester to be a distinct living person.

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Detection and dating
The beginning of pregnancy may be detected in a number of ways, including various pregnancy tests which detect hormones generated by the newly-formed placenta. Clinical blood and urine tests can detect pregnancy as early as 6-8 days after date of conception. Home pregnancy tests are personal urine tests, which normally can't detect a pregnancy until at least 12-15 days after conception. Both clinical and home tests can only detect the state of pregnancy, and cannot detect the actual date of conception.

In practice, for the purpose of giving a date for a conception (i.e. an "age" for an embryo), doctors typically date the pregnancy by "menstrual date," based on the first day of a woman's last menstrual period, as the woman reports it. Unless a woman's recent sexual activity has been limited, the exact date of conception or implantation are unknown. And absent any symptoms of morning sickness, the only visible sign of a pregnancy is often an interruption of her normal monthly menstruation cycle, (i.e. a "late period"). Hence, the "menstrual date" is simply a common educated estimate for the age of a fetus, which is an average of two weeks later than conception, (the margin of error considers 0 to 30 days after last menstruation, hence a 14 day average). The term "conception date" may sometimes be used when that date is more certain, though even medical professionals can be imprecise with their use of the two distinct terms. An unknown date for conception means that in practice the distinction between embryo and fetus is a clinical one only, and not used as to refer to stages of development of a particular pregnancy.

There are likewise finer distinctions between the concepts of fertilization (conception) and the actual state of pregnancy. In a normal pregnancy, the fertilization of the egg usually will have occurred in the Fallopian tubes or in the uterus. (In women with fertility problems, 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 implants after being transferred by a physician in the woman's uterus.

In the context of political debates regarding a proper definition of life, the terminology of pregnancy can be confusing. Because precise assessment of a pregnancy as being at the "embryo" or "fetus" stage is usually undeterminable, the terms (though more clinically precise) are less commonly used than terms like "baby" or "child." 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. In the context of personal treatment, bedside manner generally dictates that doctors make sparse use of clinical language like "fetus" and "embryo," and instead simply refer to the developing child as a "baby."

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Timeline of a typical pregnancy
Pregnancy is typically broken into three periods, or trimesters, each of about three months. While there are no hard and fast rules, these distinctions are useful in describing the changes that take place over time.

First trimester

Fertilization
Before pregnancy begins, a female oocyte (egg) must be fertilized, by male sperm in a process referred to in medicine as "fertilization," or commonly as "conception." Pregnancy is usually dated as beginning on the first day of a woman's last menstrual period. This date is used to estimate an EDD, or Estimated Date of Delivery.

Traditionally (according to Naegele's Rule, which is used to calculate the estimated date of delivery (EDD)), a human pregnancy is considered to last approximately 40 weeks (280 days) from the last menstrual period (LMP), or 37 weeks (259 days) from the date of conception. However, a pregnancy is considered to have reached term between 37 and 43 weeks. Babies born before the 37 week mark are considered premature, while babies born after the 43 week mark are considered postmature.

However, the average length of pregnancy depends on ethnic background of the mother (Caucasian women are more likely to have a longer pregnancy than other women) and if it is a first pregnancy (which tend to last longer than subsequent pregnancies). For example, a Caucasian woman's first pregnancy lasts an average 274 days from conception (288 days from the last menstrual period).

An accurate date of conception is important, because it is used in calculating the results of various prenatal tests (for example, in the triple screen test). A decision may be made to induce labour if a baby is perceived to be overdue. Due dates are only a rough estimate, and the process of accurately dating a pregnancy is complicated by the fact that not all women have 28 day menstrual cycles, or ovulate on the 14th day following their last menstrual period. Approximately 3.6% of all mothers deliver on the due date predicted by LMP, and only 4.7% give birth on the day predicted by ultrasound.

Implantation
In medicine, pregnancy is defined as beginning when a fertilized zygote becomes implanted in a woman's uterus. This occurs when the zygote then becomes embedded into the endometrium (lining of the uterus) where it forms a placenta, for the purpose of receiving essential nutrients through the uterus wall. The umbilical cord in a newborn child signifies the remnants of implantation.

Morning sickness aflicts about half of all pregnant women, typically only in the first trimester.

Second trimester
Most women feel more energised in this period, and begin to seriously put on weight. The first movement of the baby can be felt, as the baby begins to form into a recognisable shape.

Third trimester
Final weight gain takes place, and the baby begins to move regularly. This can be uncomfortable, causing symptoms like weak bladder control and back-ache.

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Medical aspects of pregnancy
Diagnostic criteria are: In a woman who has regular menstrual cycles and is sexually active, a period delayed by a few days or weeks is suggestive of pregnancy; elevated B-hcG to around 100,000 mIU/mL by 10 weeks of gestation.

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Birth
Childbirth is the process in which the baby is born. It is considered by many to be the beginning of a person's life, where age is defined relative to this event in most cultures.

A woman is considered to be in labour when she begins experiencing regular painful 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.

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Postnatal Period
Postnatal (Latin for 'after birth') is the period beginning immediately after the birth of a child and extending for about six weeks. The period is also known as postpartum and, less commonly, puerperium.

Biologically, it is the time after birth, a time in which the mother's body, including hormone levels and womb size, return to prepregnancy conditions. During the first stages of this period, the newborn also starts her or his adaptation to extrauterine life, the most significant physiological transition until death.

A woman in the Western world may leave the hospital as early as 6 hours postpartum, though the average for spontaneous vaginal delivery (SVD) is 1-2 days, and the average cesarian section postnatal stay is 3-4 days. During this time, assessment of bleeding, bowel and bladder function, and baby care happens.

The mother is assessed for tears, and given an episiotomy if necessary. Also, she may suffer from constipation or hemorrhoids, both of which would be managed, since many report these conditions to be unpleasant. The bladder is also assessed for infection, retention and any problems in the muscles.

The major focus of postpartum care is ensuring that the woman is healthy and capable of taking care of her newborn, equipped with all the information she needs about breastfeeding, reproductive health, contraception, and the imminent life adjustment.

Postpartum depression (aka baby blues) is very common, with approximately 85% of women suffering from it, potentially as early as 24 hours postpartum. It is usually limited in duration, lasting 36 to 48 hours. Treatment may be required if it lasts longer than 72 hours [1], or is associated with lack of interest in the infant, suicidal or homocidal thoughts, hallucinations, or psychotic behaviour. Approximately 10-20% of women will suffer the symptoms of major depression, and should be treated accordingly. Postpartum depression can be the response to the hormonal changes and life adjustment the woman goes through immediately after childbirth.

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