Pregnancy Week 7 – The Baby’s Progress

In pregnancy week 7 the heart will now divide into four chambers; two which are receiving blood (the atria) and the other two (the ventricles) which are now pumping blood out to the rest of the body. Special heart valves have now developed in the 4-chambered organ at the outflow of the atrium and ventricle valves to ensure that the blood only flows in one direction on each side so it does not leak back into the heart.

Pregnancy Week Seven – 4-Chambered Heart Development

The baby is now able to self sustain their own circulation The heart now has a regular beat and is continuing to develop in stages along with the pancreas, appendix and lungs. The lungs are one of the last of the body’s organs to mature which is why a baby born prematurely needs to have breathing aid.

During early fetal development your baby’s brain is forming primitive nerve-cell pathways, allowing for the first ‘twitching’ movements (that can be detected by sensitive ultrasound) as messages are being passed along his new primitive network of nerves to the muscles, but the messages are still coming from the spinal cord and not the underdeveloped brain as yet. These early twitching movements will become more fluid in the coming weeks as the brain matures further.

Glial cells (which are like natural glue) are forming in the spinal tube in order to join the nerve cells together as well as supporting and protecting them. These joined up cells are vital for allowing the transmission of messages from the brain to the rest of the body. An ‘olfactory bulb’ develops in the brain this week too which is responsible for controlling the sense of smell.

Your baby still has a thin layer of flaccid, translucent skin covering his tiny torso and already has two little nipple dots in place and teeth buds that are forming in the gum line. He may still look like a small curled up prawn and be roughly the size of a baked bean at this 7 week pregnant stage but, nonetheless, he will soldier on as his master pituitary gland, which is responsible for producing growth hormones, has now appeared and the lymphatic system that includes the tonsils, spleen, lymph nodes, thymus gland and lymphatic vessels is now beginning to develop.

There are 3 main functions of the lymphatic system:

  • To drain interstitial fluid (a tissue fluid, similar to plasma, that surrounds the cells), like when you get swollen glands, for instance.
  • It absorbs and transports fatty acids to the circulatory system
  • It also transports immune cells to and from the lymph nodes to stimulate immune response.

The gonadal ridge (or genital ridge) will be forming now too which is the precursor to the gonads from which sex cords will develop. This will give rise to sexual differentiation between the testicles of males and the ovaries of females. Primitive germ cells will arrive in the genital area ready for response to genetic instruction. The limbs are now past the critical growth stage so from here on they just need to mature and lengthen although the digits still remain webbed.

The kidneys will begin to produce urine for the first time this week. Eyelids have began to grow over the eyes and a bulging intestinal tract is now forming externally through the umbilical cord which is maturing with blood vessels in place, carrying oxygen and nutrients to the baby, This will continue, from now on, throughout the pregnancy.

By the end of pregnancy week 7 your baby will measure approximately 0.59” (15 mm) crown to rump.

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(See 7 Weeks Pregnant – The Mother’s Progress)


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