Radiological procedures have been performed for many-many years to the assist the clinician in making a diagnosis on the patient’s condition. Despites its advantages, x-rays are harmful to the human body especially the developing foetus. Hence of women of child bearing age who turn up for a radiological procedure especially that involves exposure to the abdominal or pelvic area would be routinely asked by both radiographers and radiologist on the possibility of pregnancy.

Often the foetus of a female patient who was exposed to radiation could experience congenital abnormalities due to the exposure to irradiation may even cause abnormal cellular proliferation which could result in cancer development [5]. When and where possible protective devices such as the lead shields and lead aprons are to be used to minimize the effects of radiation without affecting the region of interest. With the intention of reducing the potential harm from the exposure to radiation, several rules were suggested to protect the foetus.

What is meant by the last menstrual period (LMP)?

The last menstrual period (LMP) refers to the first day of the last menstrual period [8].

Who is asked for the LMP?

Women of child bearing age are often asked for their LMP. Women of child bearing age are generally women who are in the reproductive age group which is between puberty and menopause. During this period these women are capable of produce a child [9].

Does the enquiry of LMP apply only to married women?

As long as the woman is in the child bearing age capacity both married and unmarried women are asked for their date of LMP.

Why is the LMP asked?

The primary aim for asking the LMP is to confirm the status of pregnancy in women of child bearing age capacity.

Who asks the woman for her LMP?

  • The radiographer or the attending radiologist are required to ask the woman who is of child bearing capacity whether she is pregnant and the date of her LMP.

  • It is very important for the woman to co-operate with the radiographer or radiologist and be honest with her response.

  • The information provided by the woman is crucial in determining the possibility of pregnancy and in no way is it to be considered a harassment to the woman.

When is the LMP asked?

The radiographer and or radiologist would ask the LMP prior to performing a radiological examination so as not to irradiate the woman who may have missed her menses or may be pregnant.

How is the LMP related to radiological examination?

  • As there are low dose and high dose radiological examinations, the information on the LMP is very important.

  • Depending on the type of radiological procedure the appropriate rule (’10 Day & 28 Day rule’) is applied.

What is the ‘10 Day rule’?

The 10 Day Rule states radiological examinations can take place only during the 10 days following the onset of the menstruation and is suitable for high dose radiological examination (CT scan of the abdomen; plain x-ray of the lumbar spine). It is very important to adhere to these ground rules to minimize the detrimental effects of radiation to the unborn foetus [1].

What is the ‘28 Day rule’?

Whereas the 28 day rule, is for radiological examination that can take place throughout the cycle of 28 days until a patient experiences a missed period and suitable for low dose radiological examination (chest x-ray). Thus the focus here is more towards the missed period & the possibility of pregnancy [6]. At this juncture the patient is assumed to be pregnant unless proven otherwise through a urine for pregnancy test to confirm the status of pregnancy.


In conclusion, medical personnel such as the radiographers and radiologist play an important role in enquiring from female patients who are of child bearing age to confirm status of pregnancy. The objective is basically to limit or rather to avoid irradiating the foetus in its early stages of life due to the biological effects whether deterministic or stochastic effects.


  1. Checking The Pregnancy Status of Females of Childbearing Age. University Hospitals of Leicester, Natinal Health Services, UK. http://www.library.leicestershospitals.nhs.uk/pubscheme/Documents/Services%20we%20offer/Patient%20information/Imaging/ADULTS/Radiology%20%20Checking%20Pregnancy%20Status%20Edition%204-7125284%20-%20UHL%20Patient%20Information%20-%20Imaging.pdf

  2. Guidelines on the Protection of the Unborn Child During Diagnostic Medical Exposures http://www.rpii.ie/rpii/files/ed/ed118aac-7d24-4c98-b18c-325cc139d20f.pdf

  3. Images on 10 days & 28 days. Available online: http://www.google.com.my/imgres?start=388&biw=1024&bih=540&tbm=isch&tbnid=ZcA9_4B_wJoZ2M%3A&imgrefurl=http%3A%2F%2Fjezebel.com%2F5923069%2Ffor-a-super%2Bsmart-baby-leave-it-in-your-uterus

  4. Kementerian Kesihatan Malaysia. Guidelines for Medical Diagnostic Procedures Using X-Ray in Women of Childbearing potential

  5. Protection of Pregnant Patients during Diagnostic Medical Exposures to Ionising Radiation. Health Protection Agency, The Royal College of Radiologist & The College of Radiographers, 2009.

  6. Radiology now. The “10-Day Rule” DOI: http://dx.doi.org/10.1259/0007-1285-46-551-933 Published Online: January 28.

  7. The 28 Day Rule. Available online : http://www3.ha.org.hk/qmh/department/Clinical%20Department/Radiology/xray.htm

  8. MedicineNet.com.Definition of the Last Menstrual Period. Last reviewd 14.6.2012. http://www.medterms.com/script/main/art.asp?articlekey=13608

  9. Biology online. http://www.biology-online.org/dictionary/Childbearing_age


Last Reviewed : 9 June 2014
Writer : Pushpa Thevi Rajendran
Accreditor : Daud b. Ismail