| Course | PA 533 Obstetrics & Gynecology |
|---|---|
| Week | 2 |
| Paper type | Gestational dating exercise |
| Length | About 640 words, 5 pages |
| Format | APA 7 student paper |
| School | Chamberlain University |
| Program | Master of Physician Assistant Studies (MPAS) |
| Updated | October 2026 |
Free sample paper for PA 533 Week 2
Gestational Dating Exercise for L.M.: An LMP Date of 10 Weeks 2 Days, a Crown-Rump Length of 9 Weeks 1 Day, a Gap of Eight Days and the Rule That Says the Ultrasound Date Wins
Student Name
Chamberlain University
PA 533: Obstetrics & Gynecology
Instructor Name
Month Day, Year
Gestational Dating Exercise for L.M.: An LMP Date of 10 Weeks 2 Days, a Crown-Rump Length of 9 Weeks 1 Day, a Gap of Eight Days and the Rule That Says the Ultrasound Date Wins
Method 1: Last Menstrual Period
L.M.'s last menstrual period began on June 2. Adding 280 days gives an estimated due date of March 9. On the day of the first ultrasound, August 13, the gestational age by this method is 72 days, or 10 weeks 2 days.
The calculation takes for granted a cycle of four weeks, with the egg released halfway through, and a correctly remembered first day of bleeding. L.M. reports cycles of 32 to 35 days since weaning the first baby, and is "pretty sure" of the date because it fell on a child's birthday party. The cycle length matters: with ovulation around day 18 to 21, the LMP method will overestimate gestational age by several days.
Method 2: First-Trimester Ultrasound
Transvaginal ultrasound on August 13 measured a crown-rump length of 24 mm, the average of three measurements. That corresponds to 9 weeks 1 day. The measurement assumes that the embryo is growing at the average rate, which is most reliable in the first trimester, when growth varies least between pregnancies.
Disagreement Measured in Days
The LMP gives 10 weeks 2 days; the ultrasound gives 9 weeks 1 day. The difference is 8 days, with the ultrasound smaller.
The Rule, With a Source on It
The committee opinion on estimating the due date states that ultrasound measurement of the embryo in the first trimester, up to 13 weeks 6 days, is the most accurate method, and that between 9 weeks 0 days and 13 weeks 6 days, the due date should be changed if the ultrasound and LMP dates differ by more than 7 days (American College of Obstetricians and Gynecologists, 2017). At 9 weeks 1 day by ultrasound, L.M. falls in that band, and the difference of 8 days exceeds 7. The ultrasound date is used.
Declared Once, Then Used
Final estimated due date: March 17, based on the first-trimester ultrasound of August 13, with a crown-rump length of 24 mm. Gestational age on that day: 9 weeks 1 day. This due date is recorded once, in the problem list and the prenatal record, and is not changed by later ultrasounds, which are less accurate for dating. All later weeks in this course, including the screening schedule and the glucose test, count from it.
Why the Gap Fits the History
An 8-day gap with the ultrasound smaller fits L.M.'s long cycles, in which ovulation came later than day 14. That explanation does not decide anything; the rule decides. But it reassures that the smaller embryo reflects late ovulation rather than poor growth.
What Would Have Changed It
Had the difference been 7 days or less, the LMP date would have been kept. Had the ultrasound been done at 7 weeks, the threshold would have been 5 days. Had this been an in vitro fertilization pregnancy, the transfer date would have set the due date regardless of the ultrasound.
Who Needs to Know
The new due date was entered at the visit and L.M. was told the reason, so that L.M. would not be surprised when later appointments used a date a week later than the one L.M. had calculated at home. The change also moves the window for the glucose test and the strep culture by a week, which the scheduling staff were told.
References
American College of Obstetricians and Gynecologists. (2017). Methods for estimating the due date (Committee Opinion No. 700). Obstetrics and Gynecology, 129(5), e150-e154. https://doi.org/10.1097/AOG.0000000000002046
What the PA 533 Week 2 assignment asks for
The second week asks for a short dating exercise that shows its arithmetic. For each method, give the result with the working that produced it and the assumption that method carries, such as a regular 28-day cycle for the last menstrual period. Measure any disagreement between methods in days. Apply the published rule for when to change the due date, quoting the band of weeks and the threshold, with its source. Declare the final due date once, with the method and measurement it rests on, and use it from then on. Explain whether the gap fits the history without letting that explanation override the rule. Say what would have changed the decision. Note who needs to be told.
How this PA 533 Week 2 example is built
Method one adds 280 days to a June 2 last period for a March 9 due date and 10 weeks 2 days on August 13, noting L.M.'s 32 to 35 day cycles since weaning. Method two reports a crown-rump length of 24 mm averaged over three measurements, giving 9 weeks 1 day. The gap is calculated at 8 days. ACOG Committee Opinion 700 is quoted for changing the date when the first-trimester discrepancy exceeds 7 days between 9 weeks and 13 weeks 6 days. The final date, March 17, is declared once and used for later weeks. A section reads the gap as late ovulation without letting it decide. Counterfactuals cover a smaller gap, an earlier scan and IVF dating, and a final section informs the patient and schedulers.
Where the points sit in the PA 533 Week 2 rubric
The rubric for this exercise rewards visible working. A due date reported without the calculation behind it is the costliest omission. After that, graders want the assumption each method carries, especially regular cycles for the last menstrual period. The gap must be measured in days, not described. Credit goes to quoting the rule with its source and the correct band of weeks. Declaring the final date once and using it consistently earns marks; changing it again based on later, less accurate scans is a significant error. Explaining the gap is welcome, but letting it override the rule is marked down. Counterfactuals and communication earn smaller shares.
Common PA 533 Week 2 mistakes, and how to avoid them
Dating exercises usually go wrong when a due date appears with no arithmetic or when two dates are both kept. Send the last menstrual period, cycle history and ultrasound measurements from your case, and the exercise worked from them would show each method's calculation and assumption, measure the gap in days and apply the published redating rule with its threshold. One final date is declared and used. The history is used to explain, not decide. If your case involves an IVF pregnancy or a second-trimester scan, the rule applied changes accordingly. Recheck every date with a pregnancy wheel or calculator before you submit.
Get a PA-533 Week 2 example written to your instructions
Send the Week 2 case with whatever dates and measurements it supplies, and a custom exercise is written to it and returned inside 24 to 48 hours. The first one is free. If your section names a particular guideline for redating, include it and the example applies that rule instead of a general one.
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PA 533 Week 2 questions, answered
The case gives me a last menstrual period and nothing else. Is that enough?
It is enough to produce a week, provided the exercise says what it is trusting. Write the calculation out, name the cycle length it assumes, and state plainly what an early measurement would have added had the case supplied one. What gets marked is the visible assumption, and a paper quietly resting on a regular cycle loses the exact point the week exists to teach.
Do I have to pick one date, or can I present a range?
Pick one and defend it. A range is honest about the uncertainty and useless for everything that follows, since screening, growth and anything called late are all read against a single week. State the spread if you want to, then commit, and hold the rest of the document consistent with the week you committed to.
Is the estimated due date the point of the exercise?
No, and papers treating it that way tend to thin out. What is actually marked is the week the case sits at now, because that decides which screen is due and which findings belong. The due date falls out of the same calculation and is best written as the middle of a spread, which is how published obstetric sources describe it anyway.
Where can I find a free PA 533 Week 2 sample paper?
The full PA 533 Week 2 dating exercise is on this page, comparing an LMP date with a crown-rump length and applying the 7-day redating rule.
Why does the ultrasound date win in the PA 533 Week 2 sample?
Between 9 weeks and 13 weeks 6 days, ACOG advises changing the due date when the dates differ by more than 7 days, and these differed by 8.