Uterine environment

Contraception is the prevention of pregnancy following sexual intercourse by inhibiting sperm from reaching a mature ovum (i.e., methods that act as barriers or prevent ovulation) or by preventing a fertilized ovum from implanting in the endometrium (i.e., mechanisms that create an unfavorable uterine environment). 

The uterine environments of MZ twins will be more or less similar depending on whether there are two amnions and two chorions, two amnions and a shared chorion, or a shared amnion and chorion. 

In severe endometriosis, infertility likely results from distortion of the pelvic structure secondary to endometrial lesions, inflammation, and adhesions. In milder disease, the cause-effect relationship is more controversial. Decreased oocyte viability and/or production resulting from the altered uterine environment may be a contributing factor. ... 

Although very promising especially for the emphasis on the intra-uterine environment, the GBG hypothesis has also been refuted as subsequent studies failed to support its predictions (Bryden et al., 1994 Obrzut, 1994 Berenbaum and Denburg, 1995). In particular, a study by Gilmore et al. (2007) found the left hemisphere to be larger than the right in male neonates in comparison to female neonates, which is exactly the opposite of what would be predicted by the GBG hypothesis. 

The role of the placenta is of critical importance in the development of twins. With identical (monozygotic) twins, even a shared placenta does not guarantee uniformity and equality of the fetal environment.11 Each twin sharing a placenta is supplied by a different portion of the placenta. The sharing is almost always unequal. Delivery of maternal blood differs. The amount of space and the location of each fetus differ. Each twin has a local environment in addition to a general uterine environment. 

Rees S. Harding R. (2004). Brain development during fetal life influences of the intra-uterine environment. Neurosci. Lett. 2004 361 111—114. 

In mammals, the adaptive value of hypoxic depression is most clearly apparent in the fems. In the uterine environment a respiratory response to hypoxia would not increase O2 delivery to tissues but would increase O2 consumption. However, the peripheral chemoreceptors must have some degree of functional development in utero to deal with hypoxic challenges in the immediate postnatal period. A good solution to this problem is a well-developed central mechanism for hypoxic depression. This probably accounts for the greater-than-adult hypoxic ventilatory depression observed in the early neonate as development of the full adult ventilatory... 

When two fetuses share a placenta, the chemical comingling of steroids is overt and powerful the impact on the female fetus is devastating. In other mammals, where litters of pups are the norm, subtle differences in the uterine environment impact the developing fetus in surprising ways. For rodents and swine, the uterus is effectively a cylinder with the fetuses lined up in a row. Other than the individuals at either end of the uterus, each littermate is located in between two other individuals, and there are consequentially only three options your immediate littermates can be either two females, two males, or a male and a female. 

After insertion of an lUD, polymorphonuclear leukocytes and macrophages accumulate in the uterine cavity. These cells appear to phagocytize sperm and Hberate a blastotoxic toxin (92,93). Intrauterine devices also may create a hostile environment, perhaps because antibodies are produced that interfere with implantation of the fertilized ovum (93). 

Rein MS (2000) Advanced in uterine leiomyoma research the progesterone hypothesis. Environ Health Perspect 108 791-793... 

Spencer F, Behane Z (1982) Uterine and fetal characteristics in rats following a post-implantational exposure to permethrin. Bull Environ Contam Toxicol 29 84—88... 

Nonetheless, a sufficient dose will reduce or temporarily halt peristalsis (Brown and Taylor 1996). Some effects on esophageal peristalsis may be mediated by central mechanisms (Bieger 1984). Atropine reduces the tone and contractions of the ureter and bladder, and has antispasmodic effects on the gallbladder and bile duct. Negligible effects are produced on uterine contractions. Sweat glands are inhibited by atropine, and it can impair thermoregulation, especially in hot environments. Cardiac Effects... 

Ethanol is a vasodilator, probably as a result of both CNS effects (depression of the vasomotor center) and direct smooth muscle relaxation caused by its metabolite, acetaldehyde. In cases of severe overdose, hypothermia—caused by vasodilation—may be marked in cold environments. Ethanol also relaxes the uterus and—before the introduction of more effective and safer uterine relaxants (eg, calcium channel antagonists)—was used intravenously for the suppression of premature labor. 

The causes of many developmental abnormalities are unknown. As an example, Nelson and Holmes (1989), through a careful evaluation of approximately 70,000 children and their families, were able to account for 57% of birth defects mutations (28%), multifactorial conditions (23%), uterine factors and twinning (3%), and exposure to chemical and physical agents found in the environment (3%). Thus, the etiology of at least 43% of all birth defects could not be determined. Prevention of developmental defects depends on understanding their causes and is important in reducing the tremendous societal and financial burden. 

Siddiqui, M.K.J., Srivastava, S., Srivastava, S.P., Mehrota, P.K., Mathur, N., Tandon, I. Persistent chlorinated pesticides and intra-uterine foetal growth retardation a possible association. Int. Arch. Occup. Environ. Health 76, 75-80 (2003)... 

A more recent study carried this argument further Devlin et al (1997) criticized the conventional lumping together in quantitative genetic analyses of maternal effects (which should include intra-uterine effects) and, what they described as shared external environment. They proposed a variant on the classic type of... 

Despite its autonomy, the preimplantation embryo, from the time of fertilization of the ovum to the time of entry into the uterus, is highly influenced by its external environment. Many preimplantation embryos already have their development program corrupted by genetics or environment or both and are not viable when they enter the uterus. Other embryos, for a variety of reasons, never achieve implantation in the uterine wall and are soon destroyed. The exact percentage of seriously defective early embryos is unknown. These embryos are usually lost before a woman realizes she s pregnant and the lost embryos remain undetected. The current estimate is that 50 percent of pregnancies end in spontaneous abortion. Only about half of these losses are the result of chromosomal abnormalities.9... 

Intrauterine insemination (lUI) involves induction of ovulation, followed by transfer of motile sperm directly into the uterine cavity. This type of procedure is indicated if erectile dysfunction or male infertility (low motility, count, and/or poor morphology) has been identified, if the cervical environment is not conducive for effective sperm motility and/or sustenance, and if there are any physiological dysfunctions (93). 

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