MENSTRUAL PERIOD
PRIMIP AND MULTIP
IMPLANTATION
PRETERM
POSTTERM
GESTATION

Pregnancy is considered "at term" when gestation attains 37 complete weeks but is less than 42 (between 259 and 294 days since LMP). Events before completion of 37 weeks (259 days) are considered preterm; from week 42 (294 days) events are considered postterm. When a pregnancy exceeds 42 weeks (294 days), the risk of complications for both the woman and the fetus increases significantly, as such, obstetricians usually prefer to induce labour, in an uncomplicated pregnancy, at some stage between 41 and 42 weeks.

Accurate dating of pregnancy is important, because it is used in calculating the results of various prenatal tests (for example, in the triple test). A decision may be made to induce labour if a fetus is perceived to be overdue. Furthermore, if LMP and ultrasound dating predict different respective due dates, with the latter being later, this might signify slowed fetal growth and therefore require closer review.

 

Menstrual Period

The menstrual cycle is the scientific term for the physiological changes that can occur in fertile female humans. Overt menstruation (where there is blood flow from the uterus through the vagina) occurs in humans.
The menstrual cycle, under the control of the endocrine system, is necessary for reproduction. It is commonly divided into three phases: the follicular phase, ovulation, and the luteal phase; although some sources use a different set of phases: menstruation, proliferative phase, and secretory phase. Menstrual cycles are counted from the first day of menstrual bleeding. Hormonal contraception interferes with the normal hormonal changes with the aim of preventing reproduction.

Stimulated by gradually increasing amounts of estrogen in the follicular phase, discharges of blood (menses) slow then stop, and the lining of the uterus thickens. Follicles in the ovary begin developing under the influence of a complex interplay of hormones, and after several days one or occasionally two become dominant (non-dominant follicles atrophy and die). Approximately mid-cycle, 24–36 hours after the Luteinizing Hormone (LH) surges, the dominant follicle releases an ovum, or egg in an event called ovulation. After ovulation, the egg only lives for 24 hours or less without fertilization while the remains of the dominant follicle in the ovary become a corpus luteum; this body has a primary function of producing large amounts of progesterone. Under the influence of progesterone, the endometrium (uterine lining) changes to prepare for potential implantation of an embryo to establish a pregnancy. If implantation does not occur within approximately two weeks, the corpus luteum will involute, causing sharp drops in levels of both progesterone and estrogen. These hormone drops cause the uterus to shed its lining and egg in a process termed menstruation.

In the menstrual cycle, changes occur in the female reproductive system as well as other systems (which lead to breast tenderness or mood changes, for example). A woman's first menstruation is termed menarche, and occurs typically around age 12. The end of a woman's reproductive phase is called the menopause, which commonly occurs somewhere between the ages of 45 and 55.

	Neurological problems include apnea of prematurity, hypoxic-ischemic encephalopathy (HIE), retinopathy of prematurity (ROP), developmental disability, cerebral palsy and intraventricular hemorrhage, the latter affecting 25 percent of babies born preterm, usually before 32 weeks of pregnancy. Mild brain bleeds usually leave no or few lasting complications, but severe bleeds often result in brain damage or even death. Neurodevelopmental problems have been linked to lack of maternal thyroid hormones, at a time when their own thyroid is unable to meet postnatal needs.
	Cardiovascular complications may arise from the failure of the ductus arteriosus to close after birth: patent ductus arteriosus (PDA).
	Respiratory problems are common, specifically the respiratory distress syndrome (RDS or IRDS) (previously called hyaline membrane disease). Another problem can be chronic lung disease (previously called bronchopulmonary dysplasia or BPD).
	Gastrointestinal and metabolic issues can arise from hypoglycemia, feeding difficulties, rickets of prematurity, hypocalcemia, inguinal hernia, and necrotizing enterocolitis (NEC).
	Hematologic complications include anemia of prematurity, thrombocytopenia, and hyperbilirubinemia (jaundice) that can lead to kernicterus.
	Infection, including sepsis, pneumonia, and urinary tract infection.

As the cause of labor still remains elusive, the exact cause of preterm birth is also unsolved. In fact, the cause of 50% of preterm births is never determined. Labor is a complex process involving many factors. Four different pathways have been identified that can result in preterm birth and have considerable evidence: precocious fetal endocrine activation, uterine over-distension, decidual bleeding, and intrauterine inflammation/infection.

RISK FACTORS INCLUDE:

	Age at the upper and lower end of the reproductive years, be it more than 35 or less than 18 years of age.
	Maternal height and weight can also play a role.
	Pregnancy interval makes a difference as women with a 6 months span or less between pregnancies have a two-fold increase in preterm birth.
	Studies on type of work and physical activity have given conflicting results, but it is opined that stressful conditions, hard labor, and long hours are probably linked to preterm birth.
	Women who have undergone previous surgically induced abortions have been shown to have a higher risk of preterm birth (less than 37 weeks), as well as extreme preterm birth (less than 28 weeks).
	Adequate maternal nutrition is important. Women with a low BMI are at increased risk for preterm birth. Further, women with poor nutritional status may also be deficient in vitamins and minerals. Adequate nutrition is critical for fetal development and a diet low in saturated fat and cholesterol may help reduce the risk of a preterm delivery. Obesity does not directly lead to preterm birth; however, it is associated with diabetes and hypertension which are risk factors by themselves.
	Women with a previous preterm birth are at higher risk for a recurrence at a rate of 15–50%
	To some degree those individuals may have underlying conditions (i.e. uterine malformation, hypertension, diabetes) that persist.
	Genetic make-up is a factor in the causality of preterm birth.
	Multiple pregnancies (twins, triplets, etc.) are a significant factor in preterm birth.
	Maternal medical conditions increase the risk of preterm birth, and often labor has to be induced for medical reasons; such conditions include high blood pressure, pre-eclampsia, maternal diabetes, asthma, thyroid disease, and heart disease.
	Women with vaginal bleeding during pregnancy are at higher risk for preterm birth.
	Women with abnormal amounts of amniotic fluid, too much (polyhydramnios) or too little (oligohydramnios) are also at risk.
	Babies with birth defects are at higher risk of being born preterm.
	Finally, the use of tobacco, cocaine, and excessive alcohol during pregnancy also increases the chance of preterm delivery.

Historically efforts have been primarily aimed to improve survival and health of preterm infants (tertiary intervention). Such efforts, however, have not reduced the incidence of preterm birth. Increasingly primary interventions that are directed at all women, and secondary intervention that reduce existing risks are looked upon as measures that need to be developed and implemented to prevent the health problems of premature infants and children.