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Module 14

The heart and circulation

How a simple beating tube becomes a four-chambered heart, when the heartbeat starts and what a scan shows, and how the circulation changes with a baby's first breath.

  • 4lessons
  • 14 minreading
  • 6quiz questions
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The lessons and the quiz in this module are part of the Fertility with Kara Package. Module 1 is free to read.

Your way through Module 14

  1. Lesson 14.1 · 3 min From a tube to four chambers How the heart starts as a simple beating tube, loops into shape and is divided into four chambers, all without stopping.
  2. Lesson 14.2 · 4 min When does the heart start beating? When the first heartbeats happen, when an early scan can see them, and how the heart rate changes in the first weeks.
  3. Lesson 14.3 · 3 min Circulation before and after birth Why a baby's blood takes three shortcuts before birth, and how they close within minutes, days and weeks of the first breath.
  4. Lesson 14.4 · 4 min When the heart forms differently The most common heart differences in general terms, why the heart is vulnerable while it forms, and how differences are found.
  5. Quiz6 questions · 5 to passNot taken BadgeModule 14Earned with the quiz

Learning aims

By the end of this module you will be able to:

  • Describe how the heart tube forms, loops and is divided into four chambers.
  • Explain when the heart starts beating and what an early scan can show.
  • Describe the three shortcuts in the circulation before birth and what each one bypasses.
  • Explain how the first breaths close the shortcuts, and over what timescale.
  • Recognise the common heart differences in general terms, and compare screening and diagnosis.
  • Ask your clinic sensible questions about the timing of the first scan and about heart checks.

The module in brief

The module in brief
  • The heart forms as a tube from mesoderm in week 3 after fertilisation and starts to beat at about day 22, about 5 weeks of pregnancy.
  • In week 4 the tube loops to the right, and walls divide it into four chambers by the end of week 7 to 8; a spiralling wall splits the outflow into the aorta and the pulmonary trunk.
  • On a transvaginal scan the heartbeat is usually first seen at about 5 and a half to 6 and a half weeks of pregnancy, at about 100 beats a minute, rising to about 175 at around 8 and a half weeks.
  • Before birth, the ductus venosus, foramen ovale and ductus arteriosus route oxygen-rich blood from the placenta past the liver and the fluid-filled lungs.
  • At birth the lungs open, the foramen ovale is pressed shut within minutes to hours, and the ductus arteriosus closes within 1 to 4 days and is sealed for good over the following weeks, usually by 3 months.
  • About 9 in 1,000 babies are born with a heart difference; most have no known cause, and many are minor.
  • The detailed mid-pregnancy scan is a screening look at the heart; a specialist heart scan can give a diagnosis.
A note from Kara

Thank you for choosing to learn with me

I know you had many places to look for answers, and you chose this course. Thank you. It means a lot to me that you trust me with something this close to your heart.

Every lesson here is something I wish every couple could hear before they sit down with their clinic: how a life begins, what happens in the lab, and what the words on your report mean. Take it slowly. Short lessons, one at a time, are the way the science sinks in.

If a lesson raises a question about your own body or your own embryos, write it down and take it to your healthcare professional. That is exactly what this course is for.

Warmly, Kara

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