The baby now begins to bend her wrists. The natural position is for the limbs to be slightly bent at all joints, especially in the early stages. There is a more distinct neck area as the baby’s head is now slightly lifted off the chest.
The muscular diaphragm that will eventually enable your baby to breathe – and hiccup – is developing now.
As your baby’s lungs develop in the chest, there is nothing to separate them from the stomach, liver, and bowel, in what will later become her abdominal cavity.
In adults, the chest is separated from the abdomen by the muscular diaphragm. The diaphragm moves downwards when we breathe, and the ribs expand outwards. This process allows air to enter the lungs.
Your baby’s diaphragm forms from four in-folds of tissue. First seen at around this week of pregnancy, these folds gradually expand inwards, fusing together and closing the space by the end of this week.
In the centre of the diaphragm there are openings for the oesophagus to travel to the stomach, the aorta (the body’s main artery), and the inferior vena cava (the body’s main vein returning blood from the lower body). As pregnancy progresses, muscle fibres gradually strengthen your baby’s diaphragm, which later allows her to make breathing movements.
If you’re expecting twins or more, blood-based screening tests for Down’s can mislead, as they rely on measuring the amounts of circulating AFP (alfa-fetoprotein) and other markers, which are present in much higher levels when there’s more than one baby. That’s why the most reliable screening test is the nuchal translucency scan at 11–14 weeks.
The nuchal translucency scan is a screening test. It measures the depth of fluid under the skin in the nuchal fold at the back of the baby’s neck to assess how much fluid is present there. Excess fluid may indicate Down’s syndrome. Nuchal translucency is the most accurate way to screen for Down’s.
1. Red area shows the fluid under the skin at the back of the baby’s neck
It’s useful to be aware of the screening tests and diagnostic tests that will be on offer in the weeks to come. Your doctor or midwife will talk through the pros and cons of having each test. Some abnormalities may be detected at the 20-week scan.
Screening tests: these tests identify the “risk factor” for a particular condition, but do not confirm that your baby definitely has a condition. For example, a screening test for Down’s syndrome may give your baby a risk factor of 1:200. This means that your baby has a 1 in 200 chance of being affected by Down’s syndrome, but it does not mean that he actually has the condition.
Diagnostic tests: if screening tests reveal your baby has a high risk factor for a chromosomal abnormality, you will be offered a diagnostic test, such as amniocentesis or chorionic villus sampling, which gives a definite result as to whether or not a condition is present.
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