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Calculate pregnancy test date

Source: R/test_date.R
calculate_test_date.Rd

Calculates the recommended date for taking a pregnancy test based on a start date and type. The function supports both urine and blood tests, with blood tests typically being viable 2 days earlier than urine tests.

Usage

calculate_test_date(
  start_date,
  start_type = c("LMP", "conception", "transfer_day_3", "transfer_day_5",
    "transfer_day_6"),
  cycle = 28,
  test_type = c("urine", "blood")
)

Arguments

start_date

Date or character string representing a date, e.g. "YYYY-MM-DD". The starting reference date. The interpretation of this date depends on the start_type parameter.

start_type

character. One of:

  • "LMP": Last Menstrual Period date (default)

  • "conception": Date of conception

  • "transfer_day_3": Date of day 3 embryo transfer

  • "transfer_day_5": Date of day 5 embryo transfer

  • "transfer_day_6": Date of day 6 embryo transfer

cycle

numeric. Length of menstrual cycle in days. Only used when start_type = "LMP". Must be between 20 and 44 days. Defaults to 28 days.

test_type

character. One of:

  • "urine": Home pregnancy test (default)

  • "blood": Blood test at clinic

Value

Returns a Date object invisibly representing the recommended test date. Also prints informative messages showing:

  • The recommended date for a urine test

  • The recommended date for a blood test

Details

The test date is calculated as follows:

  1. First, the ovulation date is calculated (see calculate_due_date() for details)

  2. For urine tests: 14 days are added to the ovulation date

  3. For blood tests: 12 days are added to the ovulation date

Blood tests can typically detect pregnancy earlier than urine tests due to their greater sensitivity in detecting hCG hormone levels.

If start_date is a character string, the conversion to a Date is handled by anytime::anydate().

See also

Examples

# Calculate test date from last menstrual period
calculate_test_date("2025-01-31")
#> ℹ Estimated test date (urine): Friday, February 28, 2025
#> ℹ Estimated test date (blood): Wednesday, February 26, 2025

# Calculate for blood test from conception date
calculate_test_date(
  start_date = "5023-02-14",
  start_type = "conception",
  test_type = "blood"
)
#> ℹ Estimated test date (urine): Friday, February 28, 5023
#> ℹ Estimated test date (blood): Wednesday, February 26, 5023

# Calculate from day 5 embryo transfer
calculate_test_date(
  as.Date("2025-02-19"),
  start_type = "transfer_day_5"
)
#> ℹ Estimated test date (urine): Friday, February 28, 2025
#> ℹ Estimated test date (blood): Wednesday, February 26, 2025

# Calculate with non-standard cycle length
calculate_test_date("2025-01-31", cycle = 35)
#> ℹ Estimated test date (urine): Friday, March 07, 2025
#> ℹ Estimated test date (blood): Wednesday, March 05, 2025