Pregnancy

Pregnancy was the carrying of one or more offspring inside a womb or pregnancy sac, often by the females of a species, although male pregnancies were typical in some species. (TV: The Tsuranga Conundrum) It typically ended with abortion, miscarriage or childbirth. (TV: Dead of Night)

Some pregnancies, like ectopic pregnancies, could not result in a live birth, due to complications, (AUDIO: Moving Target) except during the Miracle, when abortions and miscarriages were made impossible. (TV: Dead of Night)

Time Lord
According to one account, all pregnancies on Gallifrey ended in miscarriage when the Pythia cursed her world with sterility. Even Rassilon's wife was said to have endured this curse. (PROSE: Cat's Cradle: Time's Crucible) This required Time Lords to adopt the asexual "Looming" process of artificial genetic reproduction. This resulted in the elimination of direct, lineal familial relations, rendering all relationships collateral. In other words, Time Lords of the same family could at most be only cousins of each other. However, the Pythia's curse did not seem to extend to off-worlders, as Leela was pregnant with Andred's baby. (PROSE: Lungbarrow)

Most other accounts did not support the idea of the Pythia's curse, showing that Time Lords had at least approximately human sexual relations. Susan, for instance, had an apparently Earth-normal pregnancy to produce her son; the extreme xenophobia present on Earth in the 2160s and 2170s would have made her a social outcast had her pregnancy been viewed as abnormal. (AUDIO: An Earthly Child) once reminisced with the Tenth Doctor about "[his] father's estate". (TV: The End of Time) As well as this, the Eighth Doctor made mention of a father, (TV: Doctor Who) as did the Tenth Doctor, (TV: The Fires of Pompeii) the Tenth Doctor mentioned a brother (TV: Smith and Jones) and the Doctor himself being a father, (TV: Fear Her, The Doctor's Daughter) while Clara Oswald mentioned the Doctor's missing children and grandchildren (TV: Death in Heaven) and mentioned her daughter (TV: The Witch's Familiar) — not to mention the fact that Susan and Alex Campbell were unambiguously identified by the Eighth Doctor as his biological grand-daughter and great-grandson. (AUDIO: An Earthly Child, Relative Dimensions) One account showed numerous groups of families with Gallifreyan children on the planet Gallifrey during the Last Great Time War. The Doctor knew by his tenth incarnation that on the last day of the Time War, 2.47 billion children were on the planet. (TV: The Day of the Doctor) The Eleventh Doctor claimed in one account that he slept in a small cot. (TV: A Good Man Goes to War) Another account showed the First Doctor as a child. (TV: Listen)

Human
Under normal circumstances, pregnancies amongst the human and humanoid were always endured by the female of the species.

Human pregnancies typically lasted nine months. (TV: The Gathering, Dark Water, The Tsuranga Conundrum) Pregnancy could remain not visible as long as three months in. (TV: Boom Town)

The Doctor's companions
Only a few of the Doctor's companions and close allies were known to be pregnant. Most were pregnant long after they stopped travelling in the TARDIS. Dodo Chaplet, for instance, was pregnant with James Stevens' baby when she was murdered by Francis Cleary. (PROSE: Who Killed Kennedy) In 2600, Bernice Summerfield became pregnant with Adrian Wall's baby when Avril Fenman temporarily took over her body. (PROSE: The Squire's Crystal, The Infernal Nexus, The Glass Prison)

One pregnancy in a companion's family can be directly attributed to the Doctor's matchmaking. After the Tenth Doctor's repeated insistence that it would be a "good match", an alternate Peter Tyler pursued a relationship with Jackie Tyler. She was pregnant with his son by the time that the Doctor summoned Rose Tyler to Bad Wolf Bay. (TV: Doomsday)

One companion was known to be pregnant while an active TARDIS traveller. After being exposed to psychic pollen, Amy Pond dreamed that she was pregnant with Rory's baby. (TV: Amy's Choice) She later fell pregnant and gave birth to River Song, conceiving her while in the Doctor's TARDIS and it was confirmed that being conceived in the Time Vortex had given River Time Lord-like characteristics. (TV: A Good Man Goes to War)

Another companion, the male Chris Cwej, was known to have impregnated a couple of women — Ishtar Hutchings and Dep — that he met while the Seventh Doctor's companion. (PROSE: Happy Endings, The Also People)

Captain Jack Harkness, a male, had fallen pregnant at an unspecified point in his life, (TV: Everything Changes) as a result of a student prank. (AUDIO: Expectant)

Harkness was later impregnated by the Empress of the Yalnix Empire with the future Ruler of the Yalnix. (AUDIO: Expectant)

On an alternate Earth, Jo Grant was pregnant when she encountered the Seventh Doctor, but lost the baby shortly afterwards. (PROSE: Blood Heat)

Rose Tyler fell pregnant with the Meta-Crisis Doctor's child Mia. The Meta-Crisis Doctor was a human hybrid incarnation of the Tenth Doctor created by biological meta-crisis. (PROSE: The Turning of the Tide)

In an alternate universe created when the Fourth Doctor went through with destroying the incubation room, Leela fell pregnant with the child of a Tesh called Gentek, placed there by the Master. The Master later captured Leela and used a cataclysmic converter to accelerate her pregnancy to full term, forcing her to give birth to the first members of a new tribe known as the Sevatesh. (AUDIO: Who Am I?)

Other humans
Queen Mary I believed that she was pregnant, but this turned out to be a false pregnancy. (AUDIO: The Marian Conspiracy)

In 1953, Marjory Kennedy was pregnant with Father Hemmings's baby when she was murdered by Walter Seacombe. (PROSE: The Canvey Angels)

James Stevens' wife Natasha was pregnant with his baby when their marriage ended. (PROSE: Who Killed Kennedy)

In 1987, Sarah Clark was pregnant with Stuart Hoskins's baby. It was in part because of this that they scheduled a wedding for this year. (TV: Father's Day)

In 1997, Tilusha Meswani became pregnant with Phil Tarrant's baby, Sanjay, which became possessed by Kelzen. (PROSE: Infinite Requiem)

Penelope Silver became pregnant with Norton Silver's baby. (PROSE: Option Lock)

In 2003, Annie Carpenter was pregnant with Michael Pembroke's baby. This fact helped them fight off the Scourge's attempts to feed on their negative emotions. (AUDIO: The Shadow of the Scourge)

In 2005, Agatha Ellis became pregnant with Godfrey's baby. (PROSE: Curtain Call)

In early 2006, the webmaster of Who is Doctor Who? was aware that there existed a reason for MP Joseph Green's recent weight gain, and that is wasn't because he was pregnant. (PROSE: Rose sighting confirmed)

In September 2006, Cathy Salt was three months pregnant when she interviewed Margaret Blaine. Blaine, who was actually Blon Fel-Fotch Passameer-Day Slitheen in disguise, planned to kill Cathy, but let her go when she learned of her condition. (TV: Boom Town)

Paul Langer told his son Clyde that he had impregnated Clyde's aunt, Melba. (TV: The Mark of the Berserker)

Donna Noble mentioned that her friend Nerys had gotten herself pregnant with twins using a turkey baster. (TV: The Doctor's Daughter)

Gwen Cooper appeared to be pregnant when a Nostrovite transferred one of its eggs into her body. (TV: Something Borrowed)

In 2009, Gwen became pregnant for real with her husband Rhys Williams' baby. This happened despite her use of contraceptive pills. Gwen blamed the various medications she had been given as a member of Torchwood Three for the failure of her contraception. (TV: Children of Earth: Day One, Children of Earth: Day Two)

Tameka Vito became pregnant with Scott's baby. (PROSE: Beyond the Sun)

In 5,000,000,053, Cheen was pregnant with Milo's baby. (TV: Gridlock)

Zara, even as a product of the Grace, became pregnant with Marek's baby on the Sphere. Her connection with her sister, Abby, meant she could feel the pains and illnesses of Zara's pregnancy. (AUDIO: The Sphere)

Kala Mandell was three weeks pregnant with her husband Niccolo Mandell's baby when his crimes were exposed. (PROSE: Mission: Impractical)

Other species
Shub-Niggurath was pregnant when she arrived into the beginning of the universe from the previous universe. She delivered her child on Polymos, which became the Nestene Consciousness. (PROSE: Synthespians™)

Quill pregnancies typically resulted in many children and often ended with the death of the mother in childbirth. Pregnancies appeared to progress rapidly and a Quill could appear heavily pregnant less than an hour after conception, (TV: The Metaphysical Engine, or What Quill Did) which was the start of a week-long hibernation period where the fetuses moved to the second womb. (TV: The Lost) In 2016, Andra'ath, otherwise known as Andrea Quill, last of the species, fell pregnant with the half-Lorr child of Ballon after having sex. (TV: The Metaphysical Engine, or What Quill Did) Andra'ath was scared of giving birth as she was aware it would result in her death. Abnormally, she conceived only one child instead of many. She fought the Shadow Kin whilst heavily pregnant with the child. (TV: The Lost)

At least one Aggedor was pregnant for nearly 100 years between the 40th and the 41st century. (AUDIO: The Bride of Peladon)

Both Gifftan males and females could fall pregnant, though males only bore male children, whilst females only bore female children. Male Gifftan pregnancy lasted for a week and progressed at a rapid speed compared to human pregnancies. Babies were gestated in a pregnancy sac that was cut open painlessly during birth. In the 67th century, Yoss Inkl was an unexpectedly pregnant Gifftan encountered by the Thirteenth Doctor and her companions just before he gave birth to his son, Avocado. (TV: The Tsuranga Conundrum)

In the year 200,000, the Face of Boe fell pregnant, expecting "Boemina". (TV: The Long Game)

Behind the scenes
A few actors made public the fact that they were pregnant while filming Doctor Who. Caroline John was probably the first, though she didn't let producer Barry Letts know about it. Nevertheless she definitely was pregnant during the filming of The Ambassadors of Death, and even performed some ill-advised stunts. (DCOM: The Ambassadors of Death) Wendy Padbury was also pregnant during the filming of The Five Doctors and had to have rather oddly-designed clothes to conceal the fact. Unfortunately, she miscarried soon after recording the story. (DOC: MM VHS 7) Tracy Ann Oberman learned of her own pregnancy during filming of her role as Yvonne Hartman in the two-parter Army of Ghosts/Doomsday. More recently, Jodie Whittaker was pregnant whilst filming her final story as the Thirteenth Doctor, The Power of the Doctor.

At least one false pregnancy was circulated by the Doctor Who production office. Mary Tamm claimed that John Nathan-Turner invented the rumour that she left the programme was because she was pregnant. In fact, though, her daughter's birthday was proof she couldn't have been pregnant while filming even the later part of her tenure.