pregnancy

Date calculations

The pregnancy package uses dates extensively. Any function argument that requires a date can either take a Date object¹, or a character string that can be parsed to a Date, e.g. "YYYY-MM-DD". The parsing is performed by anytime::anydate().

The calculate_due_date() function estimates the pregnancy due date. The start_date is interpreted differently, depending on the start_type. By default, the start_type is the last menstrual period, and the start_date is the date this started. Other start_date options, like various transfer days, are useful for those using IVF.

# invisibly returns a Date object with the estimated due date
due_date <- calculate_due_date("2025-02-24")
#> ℹ Estimated due date: Monday, December 01, 2025
#> ℹ Estimated birth period begins: November 10, 2025 (37 weeks)
#> ℹ Estimated birth period ends: December 15, 2025 (42 weeks)

Once a due date is know, how_far() tells you how far along the pregnancy is on a given date. It defaults to providing this information for the current date, but an alternative on_date can be provided. This vignette was built on September 09, 2025, so for the purposes of reading this article, that counts as “today”.

how_far(due_date = due_date)
#> ℹ You are 28 weeks and 1 day pregnant.
#> ℹ That's 11 weeks and 6 days until the due date (December 01, 2025).
#> ℹ You are 70% through the pregnancy.
how_far(on_date = "2025-09-17", due_date = due_date)
#> ℹ On September 17, 2025, you will be 29 weeks and 2 days pregnant.

The date_when() function gives the date when a certain week of pregnancy will be (or was) reached, and the duration of that date from today:

date_when(33, due_date = due_date)
#> ℹ On October 13, 2025, you will be 33 weeks pregnant.
#> ℹ That's 4 weeks and 6 days away.

By default, the output messages from how_far() and date_when() are in the second person, i.e. addressed to “you”, but there is also an option to specify another person. A value of 1 or "I" means you’ll be addressed in the first person:

how_far(due_date = due_date, person = 1)
#> ℹ I am 28 weeks and 1 day pregnant.
#> ℹ That's 11 weeks and 6 days until the due date (December 01, 2025).
#> ℹ I am 70% through the pregnancy.

Any other character string will be interpreted as a third-person name, which is useful, for example, if you’re following the pregnancy progress of a partner:

date_when(33, due_date = due_date, person = "Ruth")
#> ℹ On October 13, 2025, Ruth will be 33 weeks pregnant.
#> ℹ That's 4 weeks and 6 days away.

There is one further date-related function in the package, which is useful if you are not yet pregnant but think there’s a chance you might be, e.g. if you are undergoing fertility treatment. This is calculate_test_date(), which calculates the recommended date for taking a pregnancy test, based on start date (e.g. start of last menstural period) and test type:

calculate_test_date("2025-08-21")
#> ℹ Estimated test date (urine): Thursday, September 18, 2025
#> ℹ Estimated test date (blood): Tuesday, September 16, 2025

Tracking medications

For those who get pregnant via fertility treatment, it is likely they need to take a number of different medications to support the pregnancy. Having functionality for tracking these is useful for both practical and emotional reasons. When I was pregnant, in my personal, private pregnancy package, whenever I called my version of how_far, it would print a message with how many injections I had already endured, and how many I had left to go, which helped me get through them.

I haven’t written that functionality into how_far() in this generalised version of the pregnancy package, but I have provided a separate medications_remaining() function to keep track of medications. It requires a data frame of medications, which must have the following columns with the specified data types:

Note that if the quantity of a given medication changes during the pregnancy, you need separate rows with the start and stop dates for each quantity.

Here’s an example of what a small medications table might look like (a larger example table is provided in the package as pregnancy::medications):

# a simplified medication schedule
meds <- dplyr::tribble(
  ~medication, ~format, ~quantity, ~start_date, ~stop_date,
  "progynova", "tablet", 3, "2025-08-21", "2025-08-31",
  "progynova", "tablet", 6, "2025-09-01", "2025-09-11",
  "cyclogest", "pessary", 2, "2025-09-03", "2025-09-11",
  "clexane", "injection", 1, "2025-09-08", "2025-11-05"
)

You can then calculate the quantity of medications left to take grouped by either by medication (default) or format. By default, the calculation is for today (i.e. on_date = Sys.Date()). The resulting table assumes that the function is being called first thing in the day, i.e. before any of on_date’s medications have been taken.

medications_remaining(meds)
#> # A tibble: 3 × 2
#>   medication quantity
#>   <chr>         <int>
#> 1 clexane          58
#> 2 cyclogest         6
#> 3 progynova        18

medications_remaining(meds, group = "format")
#> # A tibble: 3 × 2
#>   format    quantity
#>   <chr>        <int>
#> 1 injection       58
#> 2 pessary          6
#> 3 tablet          18

You can specify a value other than today for on_date, as well as an until_date. This is useful if you need (as I did) to order a couple of week’s medication at the time, and have to tell the pharmacy exactly what you need:

medications_remaining(
  meds,
  on_date = "2025-09-01",
  until_date = "2025-09-14"
)
#> # A tibble: 3 × 2
#>   medication quantity
#>   <chr>         <int>
#> 1 clexane           7
#> 2 cyclogest        18
#> 3 progynova        66

Global options

It would be very tedious to have to enter a due date every time you call how_far() or date_when() over the course of a pregnancy, especially since that date is constant throughout. The same goes for the medications table required for medications_remaining().

To avoid this, the pregnancy package makes use of global options, which can be set with the set_* family of functions (set_due_date(), set_person(), set_medications()). These functions only set the options for the current R session.

To ensure the options persist across all R sessions, we suggest setting them in your .Rprofile, and give an example at the end of this vignette.

Global options can be retrieved with the get_* family of functions (get_due_date(), get_person(), get_medications()).

Any global option can be unset by calling its set_* function with the argument NULL.

# can be intentional about creating a Date object
due_date <- as.Date("2026-01-22")
set_due_date(due_date)
#> ✔ Due date set as January 22, 2026
#> ℹ Functions in the pregnancy package will now use this `due_date` option.
#> ℹ So, for this R session, you do not need to supply a value to the `due_date`
#>   argument (unless you wish to override the option).
#> ℹ To make this `due_date` option available in all R sessions, in your
#>   ".Rprofile", set `options(pregnancy.due_date = ...)`
#>   where ... is the value of `due_date`.
#> ℹ You can edit your ".Rprofile" by calling `usethis::edit_r_profile()`
#> ℹ You can retrieve the `due_date` option with `get_due_date()`,
#>   or with `getOption('pregnancy.due_date')`.

how_far()
#> ℹ You are 20 weeks and 5 days pregnant.
#> ℹ That's 19 weeks and 2 days until the due date (January 22, 2026).
#> ℹ You are 52% through the pregnancy.

set_person(1)
#> ✔ person set as 'I'
#> ℹ Functions in the pregnancy package will now use this `person` option.
#> ℹ So, for this R session, you do not need to supply a value to the `person`
#>   argument (unless you wish to override the option).
#> ℹ To make this `person` option available in all R sessions, in your
#>   ".Rprofile", set `options(pregnancy.person = ...)`
#>   where ... is the value of `person`.
#> ℹ You can edit your ".Rprofile" by calling `usethis::edit_r_profile()`
#> ℹ You can retrieve the `person` option with `get_person()`,
#>   or with `getOption('pregnancy.person')`.
how_far() # due_date option still set from previous section
#> ℹ I am 20 weeks and 5 days pregnant.
#> ℹ That's 19 weeks and 2 days until the due date (January 22, 2026).
#> ℹ I am 52% through the pregnancy.
set_person(NULL)
#> ✔ pregnancy.person option set to NULL.
#> ℹ The `person` argument will now default to "You".
how_far()
#> ℹ You are 20 weeks and 5 days pregnant.
#> ℹ That's 19 weeks and 2 days until the due date (January 22, 2026).
#> ℹ You are 52% through the pregnancy.

set_medications(pregnancy::medications)
#> ✔ medications set.
#> ℹ Functions in the pregnancy package will now use this `medications` option.
#> ℹ So, for this R session, you do not need to supply a value to the
#>   `medications` argument (unless you wish to override the option).
#> ℹ To make this `medications` option available in all R sessions, in your
#>   ".Rprofile", set `options(pregnancy.medications = ...)`
#>   where ... is the value of `medications`.
#> ℹ You can edit your ".Rprofile" by calling `usethis::edit_r_profile()`
#> ℹ You can retrieve the `medications` option with `get_medications()`,
#>   or with `getOption('pregnancy.medications')`.
medications_remaining()
#> # A tibble: 5 × 2
#>   medication   quantity
#>   <chr>           <int>
#> 1 clexane            88
#> 2 cyclogest          66
#> 3 lubion             33
#> 4 prednisolone      153
#> 5 progynova         198

options(
  pregnancy.due_date = "2025-09-16",
  pregnancy.person = "I", # addressed in first person
  pregnancy.medications = dplyr::tribble(
    ~medication, ~format, ~quantity, ~start_date, ~stop_date,
    "progynova", "tablet", 3, "2025-04-21", "2025-04-30",
    "progynova", "tablet", 6, "2025-05-01", "2025-07-11",
    "cyclogest", "pessary", 2, "2025-05-03", "2025-07-11",
    "clexane", "injection", 1, "2025-05-08", "2025-09-05"
  )
)