When does an embryo’s heart start beating?

Within the first few weeks, visualization of a developing embryo is very challenging even for experienced specialist sonographers. EPAU clinics rarely accept referrals for patients who are under 6 weeks pregnant simply because prior to this, whilst a gestational sac and even a yolk sac may be visible from 4-5 weeks, at this stage it is impossible to conclude whether the pregnancy may be viable as an embryo is simply too tiny to see. The heart beat of the embryo kicks in at around 5 weeks pregnant, and by 6 weeks pregnant both tiny embryo and heartbeat are usually visible.

What is a good heart rate at a 6 week scan?

Patients attending an EPAU clinic for an early scan are usually there because there are concerns about their pregnancy. If their ultrasound sonographer reports an embryo with a visible heartbeat, the report will state that a viable pregnancy has been seen. However, sometimes concerns are still valid, especially if the mother has a history of very heavy bleeding. The sonographer will also look at the rate of the heartbeat.  This can be very variable bearing in mind that it may only have been days since the heart began to beat. However, at 6 weeks, the average heartbeat would be expected to be 90-120 bpm. Bradycardia (slow heart rate) does not always signify a poor prognosis at this stage, however if your clinician feels that it is particularly low then that could be the case and you may be offered a rescan a week or two later.

When does an embryo start moving?

Embryos develop extremely rapidly in the first three months of pregnancy as intricate systems are established and structure evolves. A microscopic ball of cells transforms into a tiny human with recognizable arms and legs by the time of the official dating scan at around 12 weeks. The speed in which this new life progresses is quite miraculous as primitive processes begin to occur within this tiny body such as heartbeats, swallowing and of course movement. But when do these tiny movements first happen, and when would a mother first feel her baby moving?

Limb buds begin to emerge during week four, marking the first step towards arms and legs. These are not capable of co-ordinated moves but by week 9 some involuntary spontaneous twitches occur in the embryo as it changes position slightly and begins to test out the musculoskeletal system, sending important feedback back to the nervous system, thus laying the ground for future voluntary movements. These small random movements are too minimal for the mother to feel, but they can be seen during ultrasounds scans.

By 12 weeks a full range of movements have developed. Limbs can move separately and the embryo can be seen swallowing, yawning and stretching. Primitive reflexes develop such as the Moro “startle” reflex, which triggers a sudden extension of the limbs following a loud noise or other unexpected stimulus. This reflex is very pronounced in new born babies, and checking that it is present is part of the essential clinical assessments carried out shortly after birth. However it has been observed even in embryos as early as 9 weeks during ultrasounds.

The other reflex which has been observed in early embryos is the withdrawal reflex, whereby the baby begins to react to external stimuli. From around week 7 of the pregnancy, the embryo can be seen to withdraw and freeze away from any touch it experiences. This reflex is also known as the Fear Paralysis Reflex (FPR). As the fetus continues to experiment with touch and its senses become more finely tuned, the withdrawal on contact starts to lessen.

Can you feel a baby move at 9 weeks?

It is unusual for a mother to feel a baby move as early as 9 weeks, especially in a first pregnancy. Movements can usually be felt around week 18, however this varies greatly according to how sensitive the mother is, and also other issues such as her weight. Women with a low body weight tend to feel their babies move early as the abdominal wall is less thickened, and occasionally do feel their baby move as early as the end of the first trimester, although this is very rare. The first sensation of a baby moving is often described as a fluttering, and may not be felt regularly until much later in the pregnancy.

With second and subsequent pregnancies, movement is usually felt earlier. This may be because you are more aware of what to look out for, or because you have changed abdominally.

Why is it called quickening when you feel your baby move?

The word quick used to mean “alive”. In the eighteenth century a woman was often referred to as being “quick with child”. Historically, the “quickening” of a child when it if first felt move in the womb was seen as a significant point legally and morally in certain cultures. Texts have been found which date back to as early as the 1200s which refer to ancient laws whereby if a fetus was killed in the womb after quickening had been felt, then the culprit was guilty of homicide. Legal texts also show that in the early days of abortion within the UK, within English law an abortion undertaken after the point of quickening was considered a worse crime than one procured earlier. In other words, quickening was viewed as the point at which a fetus effectively was protected by legal rights.

When does an embryo start to pass urine?

Some scientists have stated that it is possible to observe an embryo’s bladder, and fluid inside it, from around weeks 9-11 on ultrasound. It is clear that swallowing is occurring around this time as the fetus ingests tiny amounts of amniotic fluid. Over the next few months this process continues regularly and by the time the baby is born, a large percentage of the amniotic fluid is actually urine it has passed.