The fetus is genetically different from its mother, and can be viewed as an unusually successful allograft. The main reason for this success is increased immune tolerance during pregnancy. Immune tolerance is the concept that the body is able to not mount an immune system response against certain triggers.During the first trimester, minute ventilation increases by 40%. The womb will grow to the size of a lemon by eight weeks. Many symptoms and discomforts of pregnancy like nausea and tender breasts appear in the first trimester.During the second trimester, most women feel more energized, and begin to put on weight as the symptoms of morning sickness subside and eventually fade away. The uterus, the muscular organ that holds the developing fetus, can expand up to 20 times its normal size during pregnancy. Braxton Hicks contractions are sporadic uterine contractions that may start around six weeks into a pregnancy; however, they are usually not felt until the second or third trimester.Final weight gain takes place during the third trimester, which is the most weight gain throughout the pregnancy. The womans abdomen will transform in shape as it drops due to the fetus turning in a downward position ready for birth. During the second trimester, the womans abdomen would have been upright, whereas in the third trimester it will drop down low. The fetus moves regularly, and is felt by the woman. Fetal movement can become strong and be disruptive to the woman. The womans navel will sometimes become convex, "popping" out, due to the expanding abdomen.
After the first 24 hours have passed, rebleeding risk remains around 40 percent over the subsequent four weeks, suggesting that interventions should be aimed at reducing this risk as soon as possible. Some predictors of early rebleeding are high systolic blood pressure, the presence of a hematoma in the brain or ventricles, poor Hunt-Hess grade (III-IV), aneurysms in the posterior circulation, and an aneurysm >10 mm in size.If a cerebral aneurysm is identified on angiography, two measures are available to reduce the risk of further bleeding from the same aneurysm: clipping and coiling. Clipping requires a craniotomy (opening of the skull) to locate the aneurysm, followed by the placement of clips around the neck of the aneurysm. Coiling is performed through the large blood vessels (endovascularly): a catheter is inserted into the femoral artery in the groin and advanced through the aorta to the arteries (both carotid arteries and both vertebral arteries) that supply the brain. When the aneurysm has been located, platinum coils are deployed that cause a blood clot to form in the aneurysm, obliterating it. The decision as to which treatment is undertaken is typically made by a multidisciplinary team consisting of a neurosurgeon, neuroradiologist, and often other health professionals.In general, the decision between clipping and coiling is made on the basis of the location of the aneurysm, its size and the condition of the person. Aneurysms of the middle cerebral artery and its related vessels are hard to reach with angiography and tend to be amenable to clipping.