pregnancy

In pregnancy: Calculate and Track Dates and Medications During Pregnancy

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)

library(pregnancy)

# save any existing options
due_date_opt <- getOption("pregnancy.due_date")
person_opt <- getOption("pregnancy.person")
medications_opt <- getOption("pregnancy.medications")

This is an R package for calculating dates and tracking medications during pregnancy and fertility treatment. It extends a private, personal package that I wrote for myself when I was pregnant. It contains functions and features that I found useful at the time, and others that I added when adapting the package for general use.

The functionality goes beyond what's offered by online pregnancy calculators and apps, plus there are no concerns (unlike with these sites and apps) about data privacy, tracking or advertising.

Date calculations

The pregnancy package uses dates extensively. Any function argument that requires a date can either take a Date object[^1], or a character string that can be parsed to a Date, e.g. "YYYY-MM-DD". The parsing is performed by anytime::anydate().

[^1]: There are many ways to create Date objects in R, including as.Date(), lubridate::ymd(), and 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")

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 r format(Sys.Date(), '%B %d, %Y'), so for the purposes of reading this article, that counts as "today".

how_far(due_date = due_date)
how_far(on_date = "2025-09-17", due_date = due_date)

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)

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)

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")

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")

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:

| Column name | Data type | Description | |----|----|----| | medication | character or factor | name of the medication | | format | character or factor | format of the medication (e.g. pill, injection) | | quantity | numeric | number of units to take per day | | start_date | Date or string representing a date, e.g. "YYYY-MM-DD" | date to start taking the medication | | stop_date | Date or string representing a date, e.g. "YYYY-MM-DD" | final date on which medication is taken |

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)

medications_remaining(meds, group = "format")

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"
)

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.

pregnancy.due_date

You can set the pregnancy.due_date option using the set_due_date() function.

When that option is set, if the due_date argument to how_far() or date_when() is NULL (the default), that option is retrieved.

set_due_date() only sets the due date for the current R session. To make this option persist (recommended), it can be added to your .Rprofile. The console output of set_due_date() provides guidance on how to do this.

# can be intentional about creating a Date object
due_date <- as.Date("2026-01-22")
set_due_date(due_date)

Then how_far() can be called without needing to specify any arguments, and date_when() only needs the target week:

how_far()

To check what the option is set to, use get_due_date().

pregnancy.person

set_person() sets the global option pregnancy.person for the current R session. If this option is set it will be retrieved to specify the value of person in how_far() and date_when(), unless it is overriden by passing another value directly to the person argument. If the option is not set, the default second-person will be used.

set_person(1)
how_far() # due_date option still set from previous section
set_person(NULL)
how_far()

pregnancy.medications

set_medications() sets the global option pregnancy.medications for the current R session.

When that option is set, if the meds argument to medications_remaining() is NULL (the default), that option is retrieved.

set_medications(pregnancy::medications)
medications_remaining()

An example .Rprofile

Taking the advice to specify the options in your .Rprofile, here's an example of what that might look like:

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"
  )
)

Note that it is best to avoid creating R objects in your .Rprofile, e.g. a medications data frame outside of the call to options(), otherwise that object will be loaded into your global environment at the start of every R session.

# reset original options
options(
  pregnancy.due_date = due_date_opt,
  pregnancy.person = person_opt,
  pregnancy.medications = medications_opt
)

pregnancy documentation built on Sept. 14, 2025, 5:09 p.m.