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What is Fetal Heart Rate Monitoring (FHR)?

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Fetal heart rate (FHR) refers to heart rate of a baby in the womb. It is also referred as fetus in medical terminology. A normal fetal heart rate usually ranges from 120 to 160 beats per minute (bpm) in the utero period. During ultrasound its measured starting from around 6 weeks and during gestation the normal range varies from 170 bpm at 10 weeks and to around 130 bpm by next quarter.

Pregnancy is one of the best times in a woman's life. The experience of carrying a tiny embryo to a full sized baby in those nine months cannot be compared to any other happiness. Since day 1, mom-to-be needs to prepare a place and create the perfect environment for the baby to nurture. But there are other things that need to be kept in mind to ensure the proper growth of a baby. The fetal heart rate is an important parameter to monitor as it can reveal a lot about the developing baby's health. The regular baby's thump heartbeat is not only rewarding but reassures parts of ultrasound, as it is a proof of well pregnancy. But if the fetal heartbeat is slower than the expected one, then it is a reason to worry.

How to monitor the fetal heartbeat during pregnancy?

The normal fetal heart rate ranges between 120 and 160 beats per minute with a variation of 5 to 25 beats per minute. You can start observing the fetal heart rate in an ultrasound after 36 days of pregnancy, but doctors usually suggest monitoring in 6th week. Absence of fetal heart rate initially doesn't imply miscarriage, as it maybe because the embryo still measures between 2 to 4 mm – which is hard for the machine to detect. Following is its significance during the crucial three trimesters of pregnancy.

First Trimester of Pregnancy

The fetal heart activity confirms the signs of pregnancy. The fetal heart rate can be seen via transvaginal sonogram after 22 days of fertilization/ ovulation or after 5 weeks and 1 day of menstrual period. In the 6th Week of pregnancy, the fetus heartbeat starts and can be seen through transvaginal ultrasound.

First Trimester of Pregnancy

If ultrasound is performed prior to 6th week, you can see a round circle in womb with a small nub on one side. During transvaginal ultrasound you can see the fetus's heart and hear the beat. In 7th week, the fetus grows from 1/17 of an inch to 1/3 of an inch – almost the size of a blueberry. Many crucial organs start developing. 7-week fetus on ultrasound looks like a yolk sac. In 8th week, the foetus grows to 3/4 of an inch. During ultrasound, you will notice a fluttering on screen and can listen to heartbeat. The uterus is about a size of an orange this week.

If the heart rate of fetal is lower in 6 to 8 weeks then there are high chances of miscarriages. Below 70 beats per minute usually means miscarriage.

During the last four weeks of first trimester, cartilage starts forming and bones begins to grow. The baby starts forming skeleton and eye structure starts progressing. The tongue begins to develop while toes and fingers lengthen but are webbed. The fetus now weighs about one gram.

By the 10th week, growth reaches to crucial point and in ultrasound, the fetal movements can be seen. To ensure everything is working properly the baby needs to move. It means from week 10 till the end of 40 weeks of gestation, baby won't be still. In some circumstances, to hear the heartbeat a fetal monitor is used.

The baby is now officially called as Fetus with the onset of 11th week as the crucial development phases are completed. Growth will be fast now and by the end of 11th week, the fetus will grow in size by 1 inch. By the end of the week, the baby will weigh a half-ounce and will be around 2 inches in length.

With 12th week, the speed of growth accelerates and the formed organ starts practicing to function. As the genitals start forming in 12th week but are not visible in the ultrasound until the 16th week of pregnancy.

Second Trimester of Pregnancy    

The 13th week signifies the beginning of second trimester. You will notice the alien look of fetus will disappear on ultrasound. The eyes will come closer and ears will shift to their place. Intestines developed within the umbilical cord moves to baby's body. Other organs such as pancreas and liver begin to function.

Second Trimester of Pregnancy

In the 14th week, you can see the movement in the chest area on ultrasound. This movement is basically breathing practice. The fetus can measure up to3½ inches in length while 2 ounces in weight. All the nutrients, calories and vitamins fetus gets from placenta. Ultrasound can also verify the heart rate if parents want to listen.

By 15th week, fetus measures between 4 to 4 ½ inches and weighs up to 3 ½ ounces. By this week, parents get anxious to know about the baby sex, which can be determined by ultrasound. It will also provide a picture of genitals.

With 4th month, the mother will experience movements in abdomen. The bones will start hardening now and the legs will be longer than arms so the movements will be kicks not punches. The anatomic ultrasound will be scheduled for 20th week. During 17th week, the fetus grows than ever before and is long as 6 inches and weighs up to 7 ounces. The heart pumps vigorously and pumps more than 25 quarts of blood.

With 18th week, baby looks like a human and weighs 8 ounces. The bowel development continues and meconium (first bowel movement) develops inside the baby. Fetal sex can be determined in ultrasound along with the arms, legs, and head and abdomen measurements.

Vernix Caseosa (it is a thin white covering which protects the skin of baby from the fluid environment of the amniotic sac) develops during 19th week.  Physicians choose to perform ultrasound after 19 weeks as most of the fetus parts can be seen clearly. At this time, the fetus will be 6 to 7 inches long and will weigh nearly 11 ounces. It is considered to be the best size of fetus measurement and photographing.

The 20th week denotes the halfway point to normal pregnancy. Baby will now weigh more and 8 or more inches longer. It is a perfect week to check the fetal anomalies. Anatomic ultrasound can lasts up to 1 hour.

21st week marks the bit slow growth process as the focus shifts to internal organs development rather than weight gain. At this time, male fetuses start dropping the testes. There is no ultrasound test required in this week as most of them are already done. In 22nd week, the fetal brain continuously grows along with the development of hearing, smell, taste, sight and touch. During this week, the physician performing ultrasound can determine the baby sex.

By the starting of 23rd week, the fetus develops remarkably so, if the early birth is detected the fetus can survive. There are high chances of impaired neonatal health while the survival is very low. In 24th week, the fetus is considered 'viable', implying the reasonable chances of survival if born prematurely. The baby keeps gaining weight.

The spine continues to strengthen in 25th week and comprises 1000 ligaments, 33 rings and 150 joints once it is completed. The closed nostrils will start to open a bit. With 26th week, the fetus grows rapidly and weighs around 2 pounds and is 9 inches in measurement. The lungs' air sacs begins to develop and secretes the surfactant (important for normal lung function) to air sacs line. The brain works hard as hearing and vision senses develops.

In the last week of second trimester, the baby's brain develops quickly and lungs continue to breathe air. Eyelids open and retinas start to develop. The physician may suggest ultrasound appointments in this week.

Third Trimester of Pregnancy

With the beginning of 28th week, the fetus grows in leaps and bounds with 90% chances of survival. The lungs functions and body fat increases to 2-3% in this week. Ultrasound is important in this week, as fetus will have a face like a human.

By 29th week, the fetus looks like a baby and its head and body are proportionate. Gaining weight is quite rapid and eyes are fully developed. Baby can now see, hear and smell. In the 30th week, baby weighs either 3 pounds or more and keeps gaining weight. Bones are now developed and bone marrow starts functioning i.e. producing red blood cells. Hearing develops and recognizes certain voices.

Third Trimester of Pregnancy

31st week marks the slow growth as the space tightens. Other body functions are perfect and now the focus is on lung development and weight gain. 32nd week marks the complete development of senses. Hair continues to growth and gaining weight slows down. In 33rd week, amniotic fluid levels are high and will remain same till the baby is born. Skin starts to red but eventually changes to pink due to fat distribution.

By 34th week, there is rapid development of brain and head size starts growing holding new brain tissues. In 35th week, the fetus weighs more than5½ pounds. The mother can see the movement through the abdomen skin that includes punching, rolling and kicking. 36th week marks the four weeks of due date and for the next few weeks the baby weight will shift towards down leaving the breath shortness for pregnant woman and little space for storage in bladder.

37th and 38th week are considered early term. The baby weighs around6½ pounds and practices breathing. The parents get confuse with the fetal breathing movements in the ultrasound, as baby isn't breathing, as there is no air in uterus. In 38th week, if the baby measures too large in ultrasound then the doctor may select to induce labor for protecting mother’s and baby’s health. Meconium develops in the fetus bowel. And once the water bag breaks, it gets clear.

The wait is worthy with 39th week. But if you are scheduled for cesarean section for any reason then there are chances that it will be performed in 39th or 40th week. With 40 weeks of pregnancy, women start to feel the time to have baby. Till 42nd week, pregnancy is considered overdue. With the onset of 41st week, the woman is prepared to give birth and starts noticing pain, swelling, fatigue and abdominal weight until the beginning of labor pain. Baby is fine until the placenta is working properly and good amniotic fluid level. In this week, if an ultrasound depicts any distress on fetus then the doctor might suggest medical induction or C-section.

In most of the pregnancies, the baby will be borne by the 42nd week. The chances of vaginal birth diminish with every passing day. C-section is best option if baby has moved to birth canal.

 Know how your little munchkin goes through various development stages in the womb. And, if you want to know your conception date then use conception calculator to know your exact conception date.

Hope this article gave you an idea about the fetal heart rate and why ultrasounds need to be doneineach stage of the pregnancy. Follow Elawoman blog to get regular updates on fertility health and treatments.

Dr. R K Sharma

About The Author

Reproductive Endocrinologist, Hysteroscopic Surgeon Dr. R K Sharma
Delhi

Dr. R K Sharma has completed MBBS and MD in Obstetrics and Gynecology from Pune University in 1981 and 1989 respectively. Dr. R K Sharma is one of the pioneers in the field of IVF treatment in India. He specializes in IUI, IVF, Embryo transfer and Hysteroscopy procedures. He is also a member of Federation of Obstetrics and Gynecology Societies of India (FOGSI). Dr. R K Sharma is presently practicing at Primus Super Specialty Hospital, Chanakyapuri, Delhi. To know more, visit elawoman.com

SOURCES AND REFERENCES:

  1. Thyroid and how it affects pregnancy pregnancy, Elawoman - 2017
  2. Top 10 early pregnancy symptoms signs of pregnancy, Elawoman - 2017
  3. Ovulation period calculator and period tracker ovulation, Elawoman - 2017
  4. Zika virus a threat to pregnant women fetus, Elawoman - 2017
  5. Size of fetus at 7 week pregnant 7-week fetus, Elawoman - 2017
  6. Know growth of 12 weeks fetus, while 12 weeks pregnant 12th week, Elawoman - 2017
  7. Symptoms at 9 weeks pregnant organs, Elawoman - 2017
  8. What changes occur, when you are 18 week pregnant 18th week, Elawoman - 2017
  9. You are 27 weeks pregnant - things to know second , Elawoman - 2017
  10. You are 27 weeks pregnant - things to know trimester, Elawoman - 2017

5 Comments

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Banira Dahal

Does having continuous FHR monitoring affect the health of the child?

Oct. 7, 2018, 5:21 p.m. 5.0

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Niraj Gautam

Fetal heart monitoring is really necessary if you are at higher risk of pregnancy.

Aug. 21, 2018, 2:48 p.m. 4.5

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Shakshi Joshi

Fetal heart rate monitors fetus heart rate and it can even help in analyzing the health condition of the fetus by this test.

Aug. 9, 2018, 6:18 p.m. 5.0

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Cassandra Federer

Great read on Fetal Heart Rate. I knew they have heart rate but didn't know about the measuring part.

June 2, 2018, 1:32 p.m. 5.0

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Kasawar Wamanrao Bapurao

March 10, 2018, 7:53 p.m. 4.5

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