PREGNANCY
Pregnancy, also known as gestation, is the time during which one or more offspring develops inside a woman. A multiple pregnancy involves more than one offspring, such as with twins.Pregnancy can occur by sexual intercourse or assisted reproductive technology. Childbirth typically occurs around 40 weeks from the last menstrual period (LMP). This is just over nine months, where each month averages 29½ days.When measured from conception it is about 38 weeks.
An embryo is the developing offspring during the first eight weeks following conception, after which, the term fetus is used until birth. Symptoms of early pregnancy may include missed periods, tender breasts, nausea and vomiting, hunger, and frequent urination.Pregnancy may be confirmed with a pregnancy test.
Pregnancy is typically divided into three trimesters.The first trimester is from week one through 12 and includes conception.Conception is when the sperm fertilizes the egg. The fertilized egg then travels down the fallopian tube and attaches to the inside of the uterus, where it begins to form the embryo and placenta. The first trimester carries the highest risk of miscarriage(natural death of embryo or fetus).The second trimester is from week 13 through 28.Around the middle of the second trimester, movement of the fetus may be felt.At 28 weeks, more than 90% of babies can survive outside of the uterus if provided with high-quality medical care. The third trimester is from 29 weeks through 40 weeks.
Prenatal care improves pregnancy outcomes. Prenatal care may include taking extra folic acid, avoiding drugs and alcohol, regular exercise, blood tests, and regular physical examinations. Complications of pregnancy may include disorders of high blood pressure, gestational diabetes, iron-deficiency anemia, and severe nausea and vomiting among others.Term pregnancy is 37 to 41 weeks, with early term being 37 and 38 weeks, full term 39 and 40 weeks, and late term 41 weeks.After 41 weeks, it is known as post term.Babies born before 37 weeks are preterm and are at higher risk of health problems such as cerebral palsy. Delivery before 39 weeks by labor induction or caesarean section is not recommended unless required for other medical reasons.
Terminology.
Associated terms for pregnancy are gravid and parous. Gravidus and gravid come from the Latin for "heavy" and a pregnant female is sometimes referred to as a gravida.[15] Gravidity is a term used to describe the number of times that a female has been pregnant. Similarly, the term parity is used for the number of times that a female carries a pregnancy to a viable stage.Twins and other multiple births are counted as one pregnancy and birth. A woman who has never been pregnant is referred to as a nulligravida. A woman who is (or has been only) pregnant for the first time is referred to as a primigravida,and a woman in subsequent pregnancies as a multigravida or as multiparous.Therefore, during a second pregnancy a woman would be described as gravida 2, para 1 and upon live delivery as gravida 2, para 2. In-progress pregnancies, abortions, miscarriages and/ or stillbirths account for parity values being less than the gravida number. In the case of a multiple birth the gravida number and parity value are increased by one only. Women who have never carried a pregnancy achieving more than 20 weeks of gestation age are referred to as nulliparous.
Signs and symptoms
The symptoms and discomforts of pregnancy are those presentations and conditions that result from pregnancy but do not significantly interfere with activities of daily living or pose a threat to the health of the mother or baby. This is in contrast to pregnancy complications. Sometimes a symptom that is considered a discomfort can be considered a complication when it is more severe. For example, nausea (morning sickness) can be a discomfort, but if, in combination with significant vomiting it causes a water-electrolyte imbalance, it is a complication known as hyperemesis gravidarum.
Common symptoms and discomforts of pregnancy include:
- Tiredness.
- Constipation
- Pelvic girdle pain
- Back pain
- 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 and pelvic veins by the uterus leads to increased hydrostatic pressure in lower extremities.
- Increased urinary frequency. A common complaint, caused by increased intravascular volume, elevated glomerular filtration rate, and compression of the bladder by the expanding uterus.
- Urinary tract infection
- Varicose veins. Common complaint caused by relaxation of the venous smooth muscle and increased intravascular pressure.
- Haemorrhoids (piles). Swollen veins at or inside the anal area. Caused by impaired venous return, straining associated with constipation, or increased intra-abdominal pressure in later pregnancy.
- Regurgitation, heartburn, and nausea.
- Stretch marks
- Breast tenderness is common during the first trimester, and is more common in women who are pregnant at a young age.
In addition, pregnancy may result in pregnancy complication such as deep vein thrombosis or worsening of an intercurrent disease in pregnancy.
Chronology
The chronology of pregnancy is, unless otherwise specified, generally given as gestational age, where the starting point is the woman's last normal menstrual period (LMP), or the corresponding age of the gestation as estimated by a more accurate method if available. Sometimes, timing may also use the fertilization age which is the age of the embryo.
Start of gestational age
According to American Congress of Obstetricians and Gynecologists, the main methods to calculate gestational age are:
- Directly calculating the days since the beginning of the last menstrual period.
- Early obstetric ultrasound, comparing the size of an embryo or fetus to that of a reference group of pregnancies of known gestational age (such as calculated from last menstrual periods), and using the mean gestational age of other embryos or fetuses of the same size. If the gestational age as calculated from an early ultrasound is contradictory to the one calculated directly from the last menstrual period, it is still the one from the early ultrasound that is used for the rest of the pregnancy.[
- In case of in vitro fertilization, calculating days since oocyte retrieval or co-incubation and adding 14 days.
Start of gestational age
According to American Congress of Obstetricians and Gynecologists, the main methods to calculate gestational age are:
- Directly calculating the days since the beginning of the last menstrual period.
- Early obstetric ultrasound, comparing the size of an embryo or fetus to that of a reference group of pregnancies of known gestational age (such as calculated from last menstrual periods), and using the mean gestational age of other embryos or fetuses of the same size. If the gestational age as calculated from an early ultrasound is contradictory to the one calculated directly from the last menstrual period, it is still the one from the early ultrasound that is used for the rest of the pregnancy.
- In case of in vitro fertilization, calculating days since oocyte retrieval or co-incubation and adding 14 days.
Physiology
Initiation
Through an interplay of hormones that includes follicle stimulating hormone that stimulates folliculogenesis and oogenesis creates a mature egg cell, the female gamete. Fertilization is the event where the egg cell fuses with the male gamete, spermatozoon. After the point of fertilization, the fused product of the female and male gamete is referred to as a zygote or fertilized egg. The fusion of male and female gametes usually occurs following the act of sexual intercourse. Fertilization can also occur by assisted reproductive technology such as artificial insemination and in vitro fertilisation.
Fertilization (conception) is sometimes used as the initiation of pregnancy, with the derived age being termed fertilization age. Fertilization usually occurs about two weeks before the next expected menstrual period.
A third point in time is also considered by some people to be the true beginning of a pregnancy: This is time of implantation, when the future fetus attaches to the lining of the uterus. This is about a week to ten days after fertilization. In this model, during the time between conception and implantation, the future fetus exists, but the woman is not considered pregnant.
Development of embryo and fetus
The sperm and the egg cell, which has been released from one of the female's two ovaries, unite in one of the two fallopian tubes. The fertilized egg, known as a zygote, then moves toward the uterus, a journey that can take up to a week to complete. Cell division begins approximately 24 to 36 hours after the male and female cells unite. Cell division continues at a rapid rate and the cells then develop into what is known as a blastocyst. The blastocyst arrives at the uterus and attaches to the uterine wall, a process known as implantation.
The development of the mass of cells that will become the infant is called embryogenesis during the first approximately ten weeks of gestation. During this time, cells begin to differentiate into the various body systems. The basic outlines of the organ, body, and nervous systems are established. By the end of the embryonic stage, the beginnings of features such as fingers, eyes, mouth, and ears become visible. Also during this time, there is development of structures important to the support of the embryo, including the placenta and umbilical cord. The placenta connects the developing embryo to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. The umbilical cord is the connecting cord from the embryo or fetus to the placenta.
After about ten weeks of gestational age, the embryo becomes known as a fetus. At the beginning of the fetal stage, the risk of miscarriage decreases sharply. At this stage, a fetus is about 30 mm (1.2 inches) in length, the heartbeat is seen via ultrasound, and the fetus makes involuntary motions.During continued fetal development, the early body systems, and structures that were established in the embryonic stage continue to develop. Sex organs begin to appear during the third month of gestation. The fetus continues to grow in both weight and length, although the majority of the physical growth occurs in the last weeks of pregnancy.
Electrical brain activity is first detected between the fifth and sixth week of gestation. It is considered primitive neural activity rather than the beginning of conscious thought. Synapses begin forming at 17 weeks, and begin to multiply quickly at week 28 until 3 to 4 months after birth.
No comments:
Post a Comment