Why Knowing Your Gestational Age Is Crucial for Safe Abortion Practices

Understanding Gestational Age

Gestational age is a critical measure in pregnancy, calculated from the first day of a woman’s last regular menstrual period (LMP). This measurement helps determine how far along a pregnancy is. According to the World Health Organization (WHO), gestational age can be directly estimated from the LMP for women with regular menstrual cycles. However, for those with irregular cycles, confirmation through physical or ultrasound examination might be necessary.

The first trimester is generally recognized as spanning from the beginning of the pregnancy until 12 to 14 weeks (1).

How Gestational Age Is Measured

Gestational age can be estimated using both sonographic and non-sonographic techniques (2).

• Non-sonographic techniques
  • LMP: You can calculate gestational age by counting the weeks since your last period. Don’t confuse LMP with the last day of your period. LMP is the first day of your last period. For example: if the current date is the 1st of March, 2024, and your LMP is the 1st of January, 2024, then, the gestational age is likely two months or roughly eight weeks. You can also use our pregnancy calculator to calculate gestational age if you know when your last menstrual period was.
    This is why understanding your menstrual cycle and knowing how to track it is crucial in sexual and reproductive education and health (4).
  • Uterine size: Physical examination of uterine enlargement provides another estimation method. To simplify this, at 12 weeks your uterus may be at the level of your pubic symphysis; at 16 weeks, it may be at the midpoint between your navel and pubic symphysis; and at 20 weeks, it may be above the level of your navel. Remember that this is not a surefire method to estimate gestational age as each person’s pregnancy growth differs.
  • Pregnancy symptoms: There are also some minor differences in pregnancy symptoms depending on the gestational age. However, it varies greatly between people. Nevertheless, some signs point positively toward pregnancy, even if gestational age is difficult to determine solely based on symptoms. You can take our quiz, “Am I pregnant?” if you’re experiencing pregnancy symptoms.
• Sonographic techniques 

  If you have the option to have an ultrasound to determine gestational age, here’s how it works across the different stages of pregnancy:

First trimester (up to 13 weeks, 6 days)

An ultrasound is most accurate during the first trimester. The crown-rump length (CRL) is measured, which is the distance from the top of your baby’s head to its bottom. This measurement is the best way to estimate how far along you are at this early stage.

Second trimester (14-28 weeks)

If you didn’t have an early ultrasound, your doctor can still estimate your baby’s age using other measurements:

• biparietal diameter (BPD) measures the width of the baby’s head;
• head circumference (HC) measures around the baby’s head to track growth;
• femur length (FL) measures the baby’s thigh bone to monitor development; and
• abdominal circumference (AC) helps check for growth problems, though it’s less reliable for dating.

Third trimester (29 weeks and beyond)

In the last trimester, other signs, like the development of your baby’s bones (ossification centers), can help determine how mature your baby is, but they’re not as reliable for dating the pregnancy as earlier measurements.

Difference Between Gestational Age and Conceptional Age

There is sometimes confusion between gestational and conceptional age. Gestational age is calculated based on LMP, while conceptional age is counted from conception. Conceptional age is generally two weeks later than gestational age and is not commonly used in clinical settings. Gestational age is more widely used in clinical settings because LMP is easier to track than the exact date of conception, while fetal age is mainly relevant when conception is precisely known. This distinction is crucial in prenatal care as gestational age is the standard for determining due dates and assessing fetal development in practice (5).

Factors Affecting the Accuracy of Gestational Age (2)

• Last menstrual period (LMP): LMP is a commonly used method, but it assumes a regular 28-day cycle. Variations in cycle length or irregular periods can reduce accuracy. Some women might confuse the first day of their last period with the last day, which can result in inaccurate estimates.
• Uterine size and physical examination: The size of the uterus can help estimate gestational age, but this method is not precise because each woman’s uterus grows at a different rate during pregnancy.
• Physical examination: Physical examination can estimate uterine size, but factors such as body type or conditions like fibroids can make it harder to accurately assess.
• Pregnancy symptoms: While some symptoms can point toward pregnancy, they vary widely from person to person. They are not reliable for determining gestational age but may help confirm pregnancy.
• Sonographic (ultrasound) techniques: A first-trimester accuracy ultrasound is most accurate in the first trimester, with crown-rump length (CRL) being the most reliable measurement for early dating. If an early ultrasound wasn’t done, other measurements during the second trimester, like biparietal diameter (BPD), head circumference (HC), femur length (FL), and abdominal circumference (AC), are used. While helpful, these are slightly less precise. The accuracy declines for ultrasounds in the third trimester; bone development (ossification centers) can help determine fetal maturity but this is less reliable for estimating gestational age than earlier measurements.

In summary, the method used to estimate gestational age, individual factors, and the timing of assessment can all influence accuracy.

Why Gestational Age Matters in Abortion

The topic of gestational age has been known to cause quite polarizing opinions in the realm of abortion politics. It has been abused in many situations to limit abortion access, especially in a post-Dobbs decision United States. The Dobbs decision was a landmark ruling by the U.S. Supreme Court in June 2022. The Court ruled that the U.S. Constitution does not guarantee a right to abortion. This decision returned the authority to regulate or prohibit abortion to individual states.

The impact of this decision has been clearly felt as evidenced by recent studies. In recent years, the number of patients traveling to other states for abortion care has doubled, reaching nearly 20% in early 2023 compared to 10% in 2020. This increase is largely due to abortion bans and restrictions following the Dobbs decision. States like Colorado, Illinois, Kansas, and New Mexico, which are near states with total abortion bans, have seen the most significant rise in out-of-state patients. The increased travel for abortion care has likely imposed significant financial and logistical challenges on individuals (6).

Additionally, access to contraceptive care appears to have worsened since the Dobbs decision. Surveys from Arizona, Iowa, New Jersey, and Wisconsin show that barriers to accessing contraception have increased and the quality of contraceptive care has declined over the past year (7).

According to WHO, the health outcomes of an abortion largely depend on factors such as the facility, the provider’s skills, the method used, the person’s health, and the gestational age of the pregnancy.

Accurate determination of gestational age is crucial for several reasons (1).

• Method selection: The choice of abortion method depends significantly on gestational age. Early pregnancies may be managed with medication or aspiration, while later pregnancies might require different procedures.
• Assessment procedures: To estimate gestational age, health-care providers typically perform a bimanual pelvic examination and an abdominal exam. Laboratory tests or an ultrasound may also be used. While an ultrasound is not routinely required, it can confirm an intrauterine pregnancy, help determine gestational age, and diagnose potential issues. Some providers find ultrasounds particularly useful before or during dilation and evacuation (D&E).
• Pain management: Adequate pain management is essential and should be offered without delay. Analgesics, local anesthesia, or conscious sedation are often used, with the need for these measures generally increasing with gestational age.
• Risk considerations: Risks associated with abortion generally increase with the duration of the pregnancy. For instance, the risk of uterine rupture, though rare, is associated with later gestational ages and a previous uterine scar, but can also occur in the absence of these risk factors. A meta-analysis found the risk of uterine rupture in women with a prior cesarean delivery having a Misoprostol-induced abortion in the second trimester to be 0.28% (1).
• Provider competence: Health-care providers must be trained and competent in assessing pregnancy duration and providing appropriate care, including accurate counseling based on the gestational age.
• Special cases: Ultrasound scanning can help identify an intrauterine pregnancy and exclude an ectopic one from six weeks of gestation, though it is not always necessary. If available, an ultrasound should ideally be conducted in a separate area from those used for prenatal care to ensure privacy and accurate diagnosis.

Safe Abortion Methods by Gestational Age

The choice of abortion method depends on gestational age and the country/region of the person receiving the abortion (9). The options include:

• a medical abortion with pills (MA) – sing the pills is safe and effective up to 13 weeks’ gestation;
• a manual vacuum aspiration (MVA) – typically, up to 14 weeks’ gestation;
• an electric vacuum aspiration (EVA) – often used up to 15 weeks’ gestation;
• a dilation and evacuation (D&E) – commonly used beyond 14 weeks’ gestation; and
• an induction abortion – generally performed for pregnancies beyond 16 weeks’ gestation.

You can also find out more regarding the viable abortion methods by gestational age.

Risks of Not Knowing Gestational Age Before Abortion

Inaccurate gestational age estimation can lead to:

• inappropriate method choice – using an unsuitable method for the gestational stage;
• increased risk of complications – there’s a higher risk of infection, bleeding, or uterine perforation with later-stage procedures;
• inadequate pain management – insufficient pain relief due to unawareness of gestational age;
• legal issues – potential legal consequences from performing abortions restricted by gestational age;
• health risks to the patient – elevated risks for certain obstetric problems like prolonged or severe bleeding, or retained products of conception;
• uninformed counseling and inacurate decision-making; and
• inadequate post-abortion care.

Is an Ultrasound Absolutely Necessary for an Abortion?

Ultrasound scanning is not routinely required for the provision of an abortion. A physical examination to assess uterine size, determine the last menstrual period, and identify symptoms of pregnancy are usually adequate (11).

This has been compounded by research that compares non-sonographic methods and sonography, where results show there is a small margin of accuracy between the two. Therefore, most women can reliably estimate gestational age using LMP, and while ultrasonography adds precision, its absence shouldn’t be a barrier to providing abortion care (10).

We are here to help you

At safe2choose, our trained counselors are here to provide compassionate and confidential support to help you make informed decisions about your pregnancy. Whether you need assistance understanding your gestational age, guidance on safe abortion methods, or information on post-abortion care, we’re here for you every step of the way. Your safety and well-being are our top priorities, and we ensure that you receive accurate information and access to safe abortion options.