Let's Have Another Baby

Wanda: Parenting is so hard and demanding, I can't stand it.
Zoe: Ma-ma.

Wanda: Let's have another one!

—Baby Blues

A phrase frequently said by one of a married couple (usually the wife) that already have at least one child, especially if they're in their 40's or late 30's, generally past the age most people want kids, but before that biological clock stops ticking. Saying this sentence guarantees one of the following:

The marriage will be breaking up very quickly.
Tonight Someone Dies
They'll agree to try to have another baby and:
- Be unable to conceive again
- They won't have another baby, but a big deal won't be made out of it. The desire to have another baby will probably never be mentioned in any other episode.

Either way, "Let's have another baby" usually indicates that they won't be doing so. Compare Fatal Family Photo. See also Unspoken Plan Guarantee.

Examples of Let's Have Another Baby include:

Anime and Manga

In the Backstory of Fruits Basket, Tohru's father suggested another baby to her mother the night before he took suddenly ill and died.

Film

In Alive Lilliana tells her husband she wants to have another baby. That night an avalanche crashes in over the fuselage, killing several people, among others Lilliana.

Literature

Stella thinks it to herself at the beginning of Nora Roberts' Blue Dahlia...right before finding out her husband died in a plane crash.
In Gone with the Wind, Scarlett is willing to do this following Bonnie's death, in the hopes that it will bring Rhett out of his grief. Unfortunately, he no longer wants anything to do with her.

Live-Action TV

Nick and Lisa on Dirty Sexy Money
Henry and Mary on My Own Worst Enemy
Full House: Jessie spends a whole episode trying to be the perfect stay-at-home dad to convince Becky they can have another baby. In the end, it's Becky covering a miraculous birth on Wake Up, San Francisco! that changes her mind. Although they never do have another baby during the course of the show...

Jessie: Just one question... when would you like to start?
Becky: Now works for me.
(to the bed, lights out)

Six Feet Under: Nate and Brenda. Granted, although it was complex and it took its while before the after-effect of this trope took effect. Nate, as a widower, already had a child from a previous marriage, but Brenda wanted her own baby. She got pregnant then miscarried the very day before their wedding. After that she got pregnant again but by then they had important marital issues, which only accelerated because of the upcoming child. They were on the verge of divorce, then Nate cheated on Brenda, and died from AMV before they could actually do anything about their relationship - though he seemed very intent on leaving her (Word of God still states he would have come back to Brenda, had he lived). So BOTH the after-effects of the trope are represented here. The trope is actually lampshaded, since when he says to Brenda to get married and have a baby, a thunder sound is heard outside - bad omen ! He never got to see his second daughter.
- Unless you count his Ghost-form, where he and her late grandfather both see her. Though its probably up to you to decide whether the ghosts on that show were the actual characters hanging around or just representations of the living characters' subconscious.
Cameron and Mitchell on the second season finale of Modern Family. Time will tell if it works out.
A unique version on One Life to Live, where in this case, the wife suggests adopting another baby in addition to the one they adopted a few years earlier. The husband refuses, stating that another child won't fix their problems. Sure enough, the marriage breaks up several weeks later.
On The Young and The Restless, Sharon suggests this to husband Nick. Subverted when (a)he refuses on the grounds that things have only just settled down following the recent premature birth of their son, and (b)the marriage does not break up. (Not then, anyway)
Home Improvement illustrated the Double Standard with this plot; in one episode, Jill wants another child, and Tim is wrong for not going along with it. In another, Tim wants another child, and he's wrong for making that decision without consulting Jill.

Newspaper Comics

In FoxTrot, Andy goes through a mid-life crisis of sorts and suggests this. Roger immediately tries to talk her out of it... only to start to recant when she suggests getting a Ferrari instead. By the end of the plot, though, Andy has given up on her mid-life crisis (but still wouldn't mind a Ferrari).
Baby Blues has Wanda swinging in and out of this one all the time.

Western Animation

Believe it or not, Patrick says this to SpongeBob SquarePants after they take care of a baby scallop.
In Family Guy, after just assisting his sister-in-law in giving birth, Peter first options to steal her baby, but then says this to Lois who agrees. That is, until they realize that they're too busy with Stewie to take care of another baby.
Played for laughs at the end of the Pinky and The Brain episode in which the two mice "have a child" together via a botched cloning attempt.

Pinky: Brain, promise we'll have another someday!

King of the Hill: Hank and Peggy get the urge to have another child after dealing the whole episode with Hank attempting to impregnate Ladybird. The next episode had Peggy failing over a dozen pregnancy tests because of Hank's narrow urethra resulting in a low sperm count, which is why Bobby is their only child. They give up afterwards. For a final, bitter twist of the knife, while they fail to have a baby, Hank's father Cotton impregnates his much-younger wife, leaving Hank and Peggy watch those two become terrible parents to a beautiful baby they don't even want.
Plays for laughs in The Simpsons. When Lisa shows her parents a video of a Brasilian orphan she sponsors, Marge finds him so cute that she says she wants another kid. Homer refuses because he hasn't lost all the weight he gained with Maggie's birth.
The Baby Blues tv series actually has Darryl say this at the end of the Christmas special.

Darryl: Let's have another baby.
The car Wanda's driving swerves.
Darryl: "I'm kidding Wanda, I'm kidding!"

In American Dad, Francine gets really desperate to have another baby when Steve starts spending more time with his girlfriend than her. It culminates with her breaking into a sperm bank and threatening to "inject" herself with George Stephanopolis' "swimmers", at which point Stan finally manages to talk her down and convince her to let go.